App for Customer ?

my custome invoice : 500 Rs

vendor invoice : 800 Rs

net off balance : 300 Rs

this is the scenario :

1. What is Payment methode/Payment methode classification for Customer

2. Customer is (income / out going payments)

3. F110 (at the time of Edit proposal -> we can see 2 line items. Kr/Dr --  we can realocate for kr but i cant realocate For Dr(customer) )

it ask payment methode iam getting errors.