Field help (PYHAMTLIN2) 

Specify the paid amount corresponding to the payment line, expressed in the payment currency.

Only payment attributes of the Bank <=> BP type can affect the Amount posted column, expressed in payment currency.
To be able to save the entry of a payment, the sum of the posted amounts of the payment must be equal to the amount of the payment specified in the BP amount field in the header information.
If it is not the case, the Unbalanced payment window is automatically displayed. This window displays the header amount, the amount of lines and the variance amount.
You can choose the terms for correcting this variance: