Hey rahul0611,
If I understand you correctly, you are asking if a user is required to pay Kshs 100 and they send Kshs 150, then what PesaPal does is credit the merchant account with the exact amount required to be paid (Kshs 100) meaning the transaction completes and then loads that Users PesaPal account with the remaining Kshs 50. If the user is not registered, what they need to do is then register on PesaPal, add the phone they used to pay with on that account, and they will be able to access the credit from their PesaPal wallet, and use it to make a payment on any website that has integrated PesaPal
This way the merchant gets what they are to be paid, and transaction is completed, and the User still has access to the extra amount they paid
If on the contrary the user pays less than they are required, then the money is only credited to their wallet which they can register in the same way as above to access, but transaction fails for merchant. In this particular case, a client can request reversal on support.pesapal.com
Hope that answers your question
