Select the payments and then go to "Action" and click "Payment Allocation".

After that one wizard opens, select details and press the "Make Payment" button.

So after that payment status changed to "Paid".

Now we try to make multiple payments of different customers.

So it gives a warning.

Now we make payment of the draft state.

So it gives a warning because posted invoice/bill only considers for the payment.

Tick the "Outstanding Payment" group.

Now select the invoices from the list view and then go to "Action" and click "Outstanding Payment".

After that one wizard opens, select partner, date, account, outstanding payments & press the "Outstanding Payment" button.

So after that payment status changed to "Paid".

Now we try to make multiple outstanding payments of different partners.

So it gives a warning.

Now we make outstanding payment of the draft invoice.

So it gives a warning because posted invoice only considers for the outstanding payment.