Document:

<PAGE>   1
                                                                    Exhibit 4.10

SERIES C PREFERRED                                    SERIES C PREFERRED

      NUMBER                                                   SHARES
      ------                                                   ------
        SPC

                             [S1 LOGO APPEARS HERE]

                                 S1 CORPORATION

INCORPORATED UNDER THE LAWS                                 SEE REVERSE SIDE FOR
OF THE STATE OF DELAWARE                                    CERTAIN LEGENDS

This Certifies that

is the owner of

    FULLY PAID AND NONASSESSABLE SHARES OF SERIES C REDEEMABLE CONVERTIBLE
                PREFERRED STOCK, PAR VALUE $0.01 PER SHARE, OF

S1 Corporation (the "Corporation"), a Delaware corporation with its principal
executive office located in Atlanta, Georgia. The shares represented by this
certificate are transferable only on the stock transfer books of the Corporation
by the holder of record hereof, or by his or her duly authorized attorney or
legal representative, upon the surrender of this certificate properly endorsed.

   This certificate is not valid unless countersigned and registered by the
Transfer Agent and Registrar.

   IN WITNESS WHEREOF, the Corporation has caused this certificate to be
executed by the signatures of its duly authorized officers and has caused its
corporate seal to be hereunto affixed.

Dated:
                                 S1 CORPORATION

                                     [SEAL]

                                       BY:

         /s/ Nancy K. Kenley                          /s/ James S. Mahan, III
               SECRETARY                                      PRESIDENT

COUNTERSIGNED AND REGISTERED:

  AMERICAN STOCK TRANSFER & TRUST COMPANY
                     (NEW YORK)     TRANSFER AGENT
                                    AND REGISTRAR

BY

                     AUTHORIZED SIGNATURE

<PAGE>   2
                                 S1 CORPORATION

   The shares represented by this certificate are issued subject to all the
provisions of the certificate of incorporation and bylaws of S1 Corporation (the
"Corporation") as from time to time amended (copies of which are on file at the
principal executive office of the Corporation), to all of which the holder by
acceptance hereof assents.

   The Corporation is authorized to issue more than one class or series of
stock. The Corporation will furnish to any shareholder, upon request and without
charge, a full statement of the powers, designations, preferences and relative,
participating, optional, or other special rights of each authorized class of
stock or series thereof and the qualifications, limitations or restrictions of
such preferences and/or rights, to the extent that the same have been fixed, and
of the authority of the board of directors to designate the same with respect to
other series. Such request may be made to the Corporation at its principal
executive office.

   The following abbreviations, when used in the inscription on the face of this
certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

<TABLE>
      <S>                                         <C>
      TEN COM -as tenants in common               UNIF GIFT MIN ACT-__________Custodian__________
      TEN ENT -as tenants by the entireties                          (Cust)       (Minor)
      JT TEN  -as joint tenants with right of                       under Uniform Gifts to Minors
               survivorship and not as tenants                      Act_______________
               in common                                                  (State)
</TABLE>

   Additional abbreviations may also be used though not in the above list.

      For value received, ________________________________________ hereby
sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE: ________________________________

________________________________________________________________________________
(PLEASE PRINT OR TYPE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE)

________________________________________________________________________________
________________________________________________________________________________
_________________________________________ shares represented by the within
certificate, and do hereby irrevocably constitute and appoint
___________________________________ Attorney to transfer the said shares on the
books of the Corporation with full power of substitution in the premises.

Dated ________________________

                   NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH
                           THE NAME AS WRITTEN UPON THE FACE OF THE CERTIFICATE
                           IN EVERY PARTICULAR, WITHOUT ALTERATION OR
                           ENLARGEMENT OR ANY CHANGE WHATEVER

  SIGNATURE(S) GUARANTEED: THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE
                           GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS
                           AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH
                           MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE
                           MEDALLION PROGRAM) PURSUANT TO S.E.C. RULE 17Ad-15.<PAGE>   1

                                                                    EXHIBIT 10.4

                                            The deleted portions of this Exhibit
                                                contain confidential information
                                         and have been filed separately with the
                                              Securities and Exchange Commission

[AMGEN(R) LOGO]                          AMENDMENT #3 TO AGREEMENT NO.  19984813
--------------------------------------------------------------------------------

This Amendment #3 to the Product Purchase Agreement No. 19984813 ("Amendment"),
by and between Amgen Inc., Amgen Center, Thousand Oaks, California 91320-1789
("Amgen") and National Medical Care, Inc., Two Ledgemeont Center-95 Hayden
Avenue, Lexington, Massachusetts, 02173 ("NMC").

WHEREAS, Amgen and NMC entered into EPOGEN(R) Product Purchase Agreement
#19984813, and as subsequently amended (the "Agreement"), and;

WHEREAS, the parties now wish to further modify this Agreement to amend the
[DELETED], to make such [DELETED] pertain solely to the second and third
calendar quarters, and to be reconciled in the fourth calendar quarter;.

NOW, THEREFORE, in consideration of the premises and of the mutual covenants,
representations and warranties set forth herein, the parties agree as follows:

SECTION 1. DEFINITIONS; REFERENCES. Unless otherwise specifically defined
herein, each term used herein, which is defined in the Agreement, shall have the
meaning assigned to such term in the Agreement. Except as amended and
supplemented hereby, all of the terms of the Agreement are incorporated herein
by reference, shall remain and continue in full force and effect and are hereby
ratified and confirmed in all respects.

SECTION 2. Amendment to Appendix A: Discount Pricing, Schedule, and Terms,
Section 5 [DELETED]. Section 5 in Appendix A shall be amended and restated in
its entirety as follows:

   5.    [DELETED]. NMC may qualify for an [DELETED] for the second and third
         calendar quarters of the year 2000 as described below.

         a.    Calculation: NMC's [DELETED] will be calculated in accordance
               with the following formula and in accordance with the [DELETED]
               schedule listed below.

                                    [DELETED] = A x B
                    where
                        A =  [DELETED]
                        B =  [DELETED]
                        C =  [DELETED]
                        D =  [DELETED]

                                 [DELETED]
                                   (C - D)/D                   B
                                   ---------                  ---
                                  [DELETED]

                The [DELETED] will be evaluated and determined based on the
                aggregate Qualified Purchases of EPOGEN(R) during the second
                calendar quarter (April 1, 2000 through June 30, 2000) and the
                third calendar quarter (July 1, 2000 through September 30,
                2000). The aggregate Qualified Purchases of EPOGEN(R) during
                these respective calendar quarters will be compared to the
                aggregate Qualified Purchases of EPOGEN(R) from the same
                calendar quarters from the previous year. If the [DELETED] set
                forth above in this

                                       1

<PAGE>   2

                                         AMENDMENT #3 TO AGREEMENT NO.  19984813
--------------------------------------------------------------------------------

             Appendix A Section 5a are attained, the [DELETED] will be paid
             within [DELETED]. At the end of the Term, and prior to the
             payment of any other incentives or rebates achieved pursuant to
             this Agreement, [DELETED].

         b.    VESTING: NMC's [DELETED] will vest on the last day of the
               second and third calendar quarters and will be paid
               [DELETED].

All other terms and conditions of the Agreement remain unchanged.

The foregoing change(s), unless otherwise specified, shall be effective from the
Commencement Date of the Agreement (January 1, 2000) and will remain in effect
for the duration of the Agreement.

Please retain one fully executed original for your records and return the other
fully executed original to Amgen.

THE PARTIES EXECUTED THIS AMENDMENT AS OF THE DATES SET FORTH BELOW.

AMGEN INC.                              NATIONAL MEDICAL CARE, INC.

Signature:    \s\ Eric Benevich         Signature:    \s\ Robert J. McGorty
Print Name:   Eric Benevich             Print Name:   Robert J. McGorty
Print Title:  Product Manager           Print Title:  Vice President of Finance
                                                      and Administration
Date:         7/17/00                   Date:         7/14/00

                                       2

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00013-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00013-of-00352.parquet"}]]