<PAGE>
                                                                  EXHIBIT 10.15

Certain confidential portions of this Exhibit were omitted by means of
asterisks in lieu of the text (the "Mark"). This Exhibit has been filed
separately with the Secretary of the Securities and Exchange Commission without
the Mark pursuant to the Company's request for confidential treatment pursuant
to the Company's request for confidential treatment pursuant to Rule 406 under
the Securities Act of 1933, as amended.


                            SECOND AMENDMENT TO THE
                 MERCHANT PROGRAM MANAGEMENT AGREEMENT BETWEEN
                                 IPAYMENT, INC.
                                      AND
                          IPAYMENT TECHNOLOGIES, INC.
                                      AND
                                 HUMBOLDT BANK

     This Second Amendment (the "Amendment") to the Merchant Program Management
Agreement between iPayment, Inc., Tennessee corporation ("IPAYMENT") and
iPayment Technologies, Inc., a California corporation and Humboldt Bank dated
September 1, 2001 (the "Agreement") is entered into as of this 3rd day of
October, 2002.

                                    RECITALS

     WHEREAS, the parties entered into the Agreement in order to govern the
relationship of the parties with respect to credit card settlement transactions
and sponsorship; and

     WHEREAS, the parties wish to amend Section 3.1 to add a new Section 3.1(h)
and to Amend Sections 8.1 and 8.2 of the Agreement;

     WHEREAS, the parties wish that the remaining terms of the Agreement remain
the same.

     NOW THEREFORE, in consideration of the foregoing premises and the mutual
covenants herein contained, the parties agree to amend the Agreement as follows:

1.   Article III, Section 3.1(c) is hereby amended to read in its entirety as
     follows:

    "(c)  Bank agrees to settle Transactions for Merchants on a non-exclusive
basis, meaning that Bank may provide the same or similar services for persons or
entities other than IPAYMENT.  Bank agrees that Bank will settle Transactions up
to and including a maximum Monthly Sales Volume of [****] so long as the ratio
of total Merchant Chargebacks (all Merchants) to total gross dollar volume (all
Merchants) is less than [****] and total Merchant Chargebacks (all Merchants)
are less than [****] per month. Notwithstanding anything contained herein, any
Merchants which are terminated by IPAYMENT shall not have their chargebacks
included in the ratios and chargeback benchmarks described above.  Furthermore,
in calculating the above ratios and chargeback benchmarks, the parties agree to
specifically exclude the merchant processing volume and chargeback levels of
European Health Concepts, a Merchant that the Bank and IPAYMENT have agreed to
terminate.  If at any time either of such benchmarks is exceeded, the parties
will cooperate in an effort to reduce Merchant Chargebacks to levels below the
benchmarks set forth in this subparagraph. In the event that the parties cannot
reduce the Merchant Chargebacks to levels below the benchmarks set forth in this
subparagraph, Bank may reduce the maximum Monthly Sales Volume it will settle
under this Agreement to such figure as Bank reasonably deems necessary, until
the parties are able to reduce such number, at which time the maximum Monthly
Sales Volume will be restored to [****].  Bank's current policies regarding the
approval of applicants to the Merchant Program are contained in Schedule A, and
Bank shall accept or reject any Customer only in conformity with Schedule A,
Bank's Merchant Application Approval Policy.  IPAYMENT shall assist Bank in
reaching its approval decision(s) by reviewing the Customer application,
verifying the information contained therein, and obtaining necessary
supplementary information concerning the Customer, when reasonably requested by
Bank.  IPAYMENT agrees that no Customer will be permitted to participate in the
Merchant Program until such Customer fulfills all of the requirements set forth
on Schedule A. Bank may amend its Merchant Application Approval Policy, in
Bank's sole discretion but only in reasonable conformity with industry standards
regarding such matters, upon thirty (30) days' written notice to IPAYMENT.  Bank
agrees to review periodically with IPAYMENT the Merchant Application Approval
Policy in order to eliminate provisions that might unnecessarily result in a
reduction of the economic benefits IPAYMENT reasonably should expect to achieve
under this Agreement.  Except as provided in subsection (h) of this Section 3.1,
Bank may, in its sole discretion, terminate any Merchant Agreement in accordance
with the terms thereof; provided, however, that in any case where a Merchant is
terminated for reasons other than actual or suspected fraud, a default of the
Merchant Agreement, or where Bank in its sole judgment determines that there is
an immediate risk of a material loss to Bank, Bank will give IPAYMENT notice of
such proposed termination such that IPAYMENT will have a reasonable opportunity
to transfer the Merchant to a different portfolio prior to Bank notifying the
Merchant of its termination."


[****] Represents material which has been redacted and filed separately with
the Commission pursuant to a request for confidential treatment pursuant to
Rule 406 under the Securities Act of 1933, as amended.
<PAGE>
2.   Article III, Section 3.1 is hereby amended by adding the following section
as a new Section 3.1(h):

     "(h) Notwithstanding anything contained herein, so long as all of the
     following are true with respect to Merchant or Merchant Account, Bank
     agrees that, except as required by the Rules, Bank shall neither terminate
     nor make any change with respect to the discount or reserve of said
     Merchant or Merchant Account that will have an adverse effect on the
     Merchant or Merchant Account without the prior written consent of
     IPAYMENT:

          "(i) The Merchant Account is not in an Association monitoring program;

          "(ii) The Merchant Account is not engaged in, or aiding and abetting,
     any illegal activity or fraud;

          "(iii) The Merchant Account is not processing Transactions where
     products are delivered or services rendered more than ninety (90) days (on
     the average, based upon Transactions of the immediately preceding three (3)
     months) following the date of the Transaction; and

          "(iv) Either (A) the Merchant Account is processing under $[****] per
     month (based upon an average of the immediately prior six months'
     Transactions), or (B) with respect to Merchant Accounts with an average
     processing of $[****] or more per month, in Bank's sole judgment the
     Merchant Account is neither experiencing significant financial
     deterioration nor is there any severe macroeconomic event causing an
     instability within merchant processing of a specific merchant or category
     of merchants in which the Merchant Account is included.

          "In the event Bank decides to terminate or make any such adverse
     change with respect to a Merchant Account with an average processing of
     $[****] or more per month solely because, in Bank's judgment, the
     conditions set forth in subparagraph (iv)(B) above are inapplicable, Bank
     shall first give IPAYMENT written notice of Bank's decision and IPAYMENT
     may, within three (3) business days of receipt of such notice, deposit into
     the IPAYMENT Reserve Account an amount equal to not less than [****]
     percent [****] of the then approved monthly processing limit for that
     specific Merchant Account, in which case Bank agrees to take no further
     action with respect to that Merchant Account solely for the reasons set
     forth in subparagraph (iv)(B) above.


[****] Represents material which has been redacted and filed separately with
the Commission pursuant to a request for confidential treatment pursuant to
Rule 406 under the Securities Act of 1933, as amended.
<PAGE>
          "Notwithstanding anything contained to the contrary herein, Bank
     covenants and agrees that until the termination of this Agreement, Bank
     will continue to operate its business and to maintain its relationship with
     IPAYMENT in significantly the same manner it has been operating its
     business as of the date of this Amendment, and that Bank will not
     significantly change any of its existing underwriting guidelines, policies
     or procedures without IPAYMENT's prior consent, which consent shall not be
     unreasonably withheld or delayed, including, but not limited to (1) changes
     in policies relating to the closing of Merchant Accounts, (2) increasing
     IPAYMENT's reserve requirements currently in place, (3) increasing any fees
     or amounts currently being paid by IPAYMENT to Bank for sponsorship and
     processing (except as such fees or amounts are imposed on Bank by a third
     party and passed through to IPAYMENT pursuant to this Agreement), (4)
     changes in criteria for withholding IPAYMENT's funds, (5) amending the
     existing underwriting guidelines or underwriting procedures, or (6) taking
     any other actions or failing to take any actions which are not consistent
     with the way Bank and IPAYMENT conduct their business as of the date of
     this Amendment. Each party agrees that it will in good faith seek to
     resolve any differences that may arise between the parties under this
     Agreement to the extent the same are not expressly covered by this
     Agreement, including this Amendment. Bank acknowledges that IPAYMENT has
     relied on this statement in entering into this Amendment and that Bank's
     material breach of this covenant may cause material harm to the business of
     IPAYMENT and its related parent and subsidiary corporations."

3.   Article VIII, Section 8.1 is hereby amended to read in its entirety as
     follows:

     "8.1. Term. This Agreement will become effective on the Effective Date, and
     unless terminated earlier in accordance with the provisions of this
     Agreement or by IPAYMENT in its sole discretion, will expire on April 29,
     2003."

4.   Article VIII, Section 8.2 hereby amended to read in its entirety as
     follows:

     "8.2. Termination. Notwithstanding Section 8.1 the parties will have the
     following rights and obligations:

     "(a) Ability to Perform. If Visa or MCI prohibits IPAYMENT from providing,
     or prohibits Bank from allowing IPAYMENT to provide, the services set forth
     in this Agreement, or if Bank becomes insolvent or is no longer an
     Acquiring Member of Visa or MCI, this Agreement will automatically and
     immediately terminate. In addition, Bank may terminate this Agreement upon
     ninety (90) days' written notice to IPAYMENT in the event Bank becomes
     subject to any change in a statute, law, rule, regulation, policy or other
     official pronouncement of any state or federal government entity regulatory
     agency or of VISA or MCI which would prohibit Bank from continuing the
     business described in this Agreement.

     "(b) Obligations Upon Expiration or Termination. Immediately following the
     expiration or earlier termination of this Agreement for any reason,
     IPAYMENT will contract with a third party Acquiring Member to perform
     Bank's duties under this Agreement and Bank, upon he effective date of the
     assignment and assumption agreements entered into at such time, will assign
     the Merchant Agreements, including all Merchant files and records (paper
     and fiche), BINs, ICAs and databases relating to such Merchants and
     Merchant Agreements, and all related deposit accounts to said third party
     Acquiring Member at no expense to IPAYMENT other than the actual cost of
     copying, shipping, supplies, and any related Association, Network and
     Processor fees. Pending such assignment, the rights and

<PAGE>
     obligations of the parties (including, without limitation, the rights and
     obligations relating to compensation under Article V hereof) shall continue
     to be governed by this Agreement in all respects."

5.   As hereby amended and supplemented the Agreement shall remain in full
force and effect.


     IN WITNESS WHEREOF, the parties hereto have executed this Amendment to the
Agreement as of the Effective Date above:



HUMBOLDT BANK                        By:   /s/ illegible
                                           -----------------------------

                                     Its:            CEO
                                           -----------------------------

                                     Date:          10/3/02
                                           -----------------------------



IPAYMENT, INC.                      By:    /s/ Gregory Daily
(a Tennessee corporation)                  -----------------------------

                                     Its:
                                           -----------------------------

                                     Date:
                                           -----------------------------



IPAYMENT TECHNOLOGIES, INC.          By:   /s/ Gregory Daily
                                           -----------------------------

                                     Its:
                                           -----------------------------

                                     Date:
                                           -----------------------------