This task should be performed by the Paymee install program. However with certain user configurations, the the install program may fail & will yield a error message to refer to this Help topic. To manually register the Paymee Addin for Excel (any version):
1) Close all instances of Excel.
2) Then open a single blank Excel session (start a blank Excel if no Excel file is active).
3) Enter keystrokes: Alt, T, I
4) If Paymee is not listed, select Browse... then select the file Paymeev4.xla from the Paymee installation directory (by default: C:\Program Files\Sapro Systems Paymeev4 or C:\Program Files (x86)\Sapro Systems Paymeev4).
5) Close Excel so that the setting is saved.