<PAGE>

                                                                     EXHIBIT 4.3


                AMENDMENT NO. 1 TO THE INVESTORS' RIGHT AGREEMENT

         THIS AMENDMENT NO. 1 TO THE INVESTORS' RIGHT AGREEMENT (the
"Amendment") is dated March 19, 2002 by and among iPAYMENT HOLDINGS, INC., a
Tennessee corporation (the "Company"), those persons identified on Exhibit A
attached hereto (collectively, the "Initial Investors" and each individually an
"Initial Investor"); and those persons identified on Exhibit B attached hereto
(collectively, the "New Investors" and each individually a "New Investor") (the
Initial Investors and the New Investors shall collectively be referred to herein
as the "Investors" and each individually an "Investor").

                                    RECITALS

         WHEREAS, the Company and the Initial Investors entered into a
Investors' Rights Agreement, dated as of April 12, 2001 (the "Agreement");

         WHEREAS, Petra Mezzanine Fund, L.P. was a party to the Agreement, but
no longer has any rights under the Agreement pursuant to the Acknowledgement and
Amendment to Loan Documents, dated as of July 31, 2001;

         WHEREAS, the Company has entered into an Agreement and Plan of Merger,
dated as of the date hereof, by and between the Company, iPayment Acquisition
Sub, Inc., and E-Commerce Exchange, Inc. (the "Merger Agreement"), whereby the
New Investors shall receive an aggregate principal amount of subordinated
convertible notes in the amount of $15,000,000 (the "Notes");

         WHEREAS, as a condition to the Merger Agreement, the Company agreed to
cause this Amendment to be executed and delivered; and

         WHEREAS, the Company and the Investors desire to amend the Agreement as
set forth in this Amendment.

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the foregoing, for other good and
valuable consideration and the respective representations, warranties,
covenants, agreements and conditions contained herein, the receipt and
sufficiency of which are hereby acknowledged, the parties hereby agree as
follows:

1. The term "Investors" as defined in the Agreement and the corresponding list
of persons identified on Exhibit A to the Agreement is hereby amended and
restated to include all of the persons identified on Exhibits A and B attached
to this Amendment only for Sections 1, 2, 3, 4 and 6 of the Agreement. The term
"Initial Investors" shall mean the persons identified on Exhibit A attached to
this Amendment and the term "New Investors" shall mean the persons identified on
Exhibit B attached to this Amendment. The New Investors shall be a party to the
Agreement only for purposes of Sections 1, 2, 3, 4 and 6 of the Agreement.



<PAGE>



2.       Section 1.1 of the Agreement shall be amended to include the following:

         1.1 Definitions. "Notes" shall mean the subordinated convertible notes
         in an aggregate principle amount of $15,000,000 issued to the New
         Investors in consideration of the Company's acquisition of E-Commerce
         Exchange, Inc. on March 19, 2002.

3.       Section 3.6 of the Agreement shall be amended and restated as follows:

         3.6 Termination of Covenants. All covenants of the Company contained in
         Section 3 of this Agreement shall expire and terminate upon the closing
         of the Initial Offering; provided that the covenants of the Company
         contained in Section 3 of this Agreement shall terminate with regards
         to the New Investors on the earlier to occur of (i) an Initial
         Offering, (ii) the payment of the Notes in full (if not converted in
         whole or in part) and (iii) the New Investors and their affiliates
         ceasing to hold at least 60% of the iPayment Underlying Common Stock
         (as defined in the Merger Agreement).

4.       Section 4.1.1 of the Agreement shall be amended and restated as
         follows:

         4.1.1 Subsequent Offerings. Each Investor shall have a right of first
         refusal to purchase its pro rata share of all Equity Securities, as
         defined below, that the Company may, from time to time, propose to sell
         and issue after the date of this Agreement, other than the Equity
         Securities excluded by Section 4.4 hereof. Each Investor's pro rata
         share is equal to the ratio of (A) the number of shares of the
         Company's Common Stock of which such Investor is deemed to be a holder
         immediately prior to the issuance of such Equity Securities, assuming
         full conversion of the Preferred Stock and the Notes and exercise of
         the Warrants held by such Investor to (B) the total number of shares of
         the Company's outstanding Common Stock immediately prior to the
         issuance of the Equity Securities. The term "Equity Securities" shall
         mean (i) any Common Stock, Preferred Stock or other security of the
         Company, (ii) any security convertible, with or without consideration,
         into any Common Stock, Preferred Stock or other security (including any
         option to purchase such a convertible security), (iii) any security
         carrying any warrant or right to subscribe to or purchase any Common
         Stock, Preferred Stock or other security or (iv) any such warrant or
         right.

5.       Section 4.2 of the Agreement shall be amended and restated as follows:

         4.2 Termination of Rights of First Refusal. The rights of first refusal
         established by this Section 4 shall not apply to, and shall terminate
         upon the closing of, an Initial Offering; provided that the rights of
         first refusal established by this Section 4 of this Agreement shall
         terminate on the earlier to occur of, (i) with regard to a New Investor
         on an individual basis, the second occasion on which such New Investor
         is offered the opportunity to exercise its rights under Section 4.1 of
         the Agreement and such New Investor elects not to exercise such right,
         (ii) with regard to the New Investors taken as a whole, an Initial
         Offering, (iii) with regard to the New Investors taken as a whole, the
         payment of the Notes in full (if not converted in whole or in part) and
         (iv) with regard to the New Investors taken as a whole, the New
         Investors and their affiliates ceasing to hold at least 60% of the
         iPayment Underlying Common Stock.



                                       2
<PAGE>

6.       Section 4.4(a) of the Agreement shall be amended and restated as
         follows:

         4.4 Excluded Securities. The rights of first refusal established by
this Section 4 shall have no application to the issuance of any of the following
Equity Securities:

                  (a) shares of Common Stock (and/or options, warrants or other
         Common Stock purchase rights issued pursuant to such options, warrants
         or other rights) issued or to be issued to employees, officers or
         directors of, or consultants or advisors to the Company or any
         subsidiary, pursuant to stock purchase or stock option plans or other
         arrangements that are approved by the Board of Directors;

                  (b) shares of Common Stock issued pursuant to any rights or
         agreements outstanding as of the date of this Agreement, and shares of
         Common Stock issued pursuant to any such rights or agreements granted
         after the date of this Agreement; provided that the rights of first
         refusal established by this Section 4 applied with respect to the
         initial sale or grant by the Company of such rights or agreements;

                  (c) any Equity Securities issued for consideration other than
         cash pursuant to a merger, consolidation, acquisition or similar
         business combination approved by the Board of Directors and the Initial
         Investors to the extent such approval of the Initial Investors is
         required under the Loan and Security Agreement, the Warrants of even
         date herewith and the Articles of Amendment to the Charter of the
         Company as filed on the date hereof;

                  (d) shares of Common Stock issued in connection with any stock
         split, stock dividend or recapitalization by the Company;

                  (e) shares of preferred stock of the Company or warrants to
         purchase Common Stock of the Company, and the Common Stock issued upon
         conversion or exercise of such preferred stock or warrants, issued
         pursuant to the Stock Purchase Agreement or the Loan and Security
         Agreement;

                  (f) shares of Common Stock issued upon an Initial Offering;

                  (g) shares of Common Stock issued in connection with any
         anti-dilution rights granted to any of the Investors;

                  (h) shares of Common Stock issued pursuant to the offering of
         shares of Common Stock to the shareholders of iPayment Technologies,
         Inc. ("iPayment") in exchange for shares of Common Stock of iPayment,
         on the same terms as described in the Common Stock Exchange Agreement
         of even date herewith, and any shares of Common stock issued pursuant
         to the Company's planned minority stock exchange with the remaining
         shareholders of iPayment;

                  (i) shares of Common Stock issued to 1st National Processing,
         Inc. in connection with its or its subsidiary's acquisition by the
         Company;

                  (j) the Notes issued to the New Investors; or

                  (k) shares of Common Stock issued upon the conversion of the
         Notes.



                                       3
<PAGE>

7. Except as expressly set forth in this Amendment, the terms and conditions of
the Agreement shall remain in place and shall not be altered, amended or changed
in any manner whatsoever, except by any further amendment to the Agreement made
in accordance with the terms of the Agreement, and such terms and conditions
shall be incorporated herein by this reference.

8. The term "Agreement" as defined in the Agreement is amended to include this
Amendment.

9. This Amendment may be executed in any number of counterparts and by different
parties to this Amendment in separate counterparts, each of which when so
executed shall be deemed to be an original and all of which taken together shall
constitute one and the same Amendment.

10. Except as modified and amended hereby, the Agreement shall remain in full
force and effect.



                                       4
<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
signed by an individual thereto duly authorized, all on the date first written
above.



                             COMPANY:

                             iPAYMENT HOLDINGS, INC.


                             By:   /s/ Gregory S. Daily
                                   -----------------------------
                             Name:      Gregory S. Daily
                                   -----------------------------
                             Title:
                                   -----------------------------


                             INITIAL INVESTORS:

                             FIRST AVENUE PARTNERS, L.P.

                             By:      Front Street, LLC, GP, its General Partner


                             By:   /s/ David Wilds
                                   -----------------------------
                             Name:      David Wilds
                                   -----------------------------
                             Title:   Chief Manager
                                   -----------------------------

                             HARBINGER MEZZANINE PARTNERS, L.P.

                             By:      Harbinger Mezzanine GP, LLC,
                                      its General Partner

                                      By:     Harbinger Mezzanine Manager, Inc.,
                                              its Manager


                             By:   /s/ John Harrison
                                   ----------------------------
                             Name:      John Harrison
                                   ----------------------------
                             Title:   Director
                                    ---------------------------


                             CAYMAS, LLC


                             By:   /s/ Carl Grimstad
                                   ----------------------------
                             Name:      Carl Grimstad
                                   ----------------------------
                             Title:
                                   ----------------------------



                                       5
<PAGE>




                                /s/ Gregory S. Daily
                              ---------------------------------
                              Gregory S. Daily


                                /s/ Carl Grimstad
                              ---------------------------------
                              Carl Grimstad

                              STREAM FAMILY LIMITED PARTNERSHIP


                              By:   /s/ Bruce N. Kirkpatrick
                                  -----------------------------
                              Name:      Bruce N. Kirkpatrick
                                    ---------------------------
                              Title:   Secretary - Treasurer
                                    ---------------------------------
                                     Matilda Stream Management, Inc.,
                                     Managing General Partner

                              NEW INVESTORS:

                              SUMMIT VENTURES V, L.P.

                              By:      Summit Partners V, L.P.,
                                       its General Partner

                              By:      Summit Partners, LLC,
                                       its General Partner

                              By:        /s/ Peter Chung
                                       ------------------------
                              Name:      Peter Chung
                                       ------------------------
                              Title:   Member


                              SUMMIT VENTURES V COMPANION FUND, L.P.

                              By:      Summit Partners V, L.P.,
                                       its General Partner

                              By:      Summit Partners, LLC,
                                       its General Partner

                              By:        /s/ Peter Chung
                                       ------------------------
                              Name:      Peter Chung
                                       ------------------------
                              Title:   Member

                              SUMMIT V ADVISORS FUND, L.P.



                                       6
<PAGE>

                              By:      Summit Partners V, L.P.,
                                       its General Partner

                              By:      Summit Partners, LLC,
                                       its General Partner

                              By:        /s/ Peter Chung
                                       ------------------------
                              Name:      Peter Chung
                                       ------------------------
                              Title:   Member


                              SUMMIT V ADVISORS (QP) FUND, L.P.

                              By:      Summit Partners V, L.P.,
                                       its General Partner

                              By:      Summit Partners, LLC,
                                       its General Partner

                              By:        /s/ Peter Chung
                                       ------------------------
                              Name:      Peter Chung
                                       ------------------------
                              Title:   Member


                              SUMMIT INVESTORS III, L.P.


                              By:        /s/ Peter Chung
                                       ------------------------
                              Name:      Peter Chung
                                       ------------------------
                              Title:   Authorized Signatory


                              RANDOLPH STREET PARTNERS


                              By:        /s/ Ted H. Zook
                                       ------------------------
                              Name:      Ted H. Zook
                                       ------------------------
                              Title:     Authorized Signatory
                                       ------------------------


                              RANDOLPH STREET PARTNERS 1998 DIF, LLC


                              By:        /s/ Ted H. Zook
                                       ------------------------
                              Name:      Ted H. Zook
                                       ------------------------


                                       7
<PAGE>

                              Title:     Authorized Signatory
                                       ------------------------


                              SYCR INVESTMENT FUND I, LLC


                              By:        /s/ Stephen T. Freeman
                                       -------------------------
                              Name:      Stephen T. Freeman
                                       -------------------------
                              Title:     Manager
                                       -------------------------

                              By:        /s/ Lawrence B. Cohn
                                       -------------------------
                              Name:      Lawrence B. Cohn
                                       -------------------------
                              Title:     Manager
                                       -------------------------








                                       8