When payment method is updated in billing schedule, it is not coming at invoice proposal level. Neither option of payment method is there at project contract level.

Currently invoice proposal takes payment method from customer master only. And option is only there at invoice proposal level to modify it. This is against the general design. For payment terms contact, customer requisition all these can be mentioned at project contract level and then it comes at invoice proposal level. It is difficult to understand why payment method is not using the same design. 

This will help all customer where payment method changes based on different contract.