Inform the counterpart via the transaction chat that the amount of funds received is different from the agreed amount.

Higher amount received: 

1. Ask what payment concept to set for the refund of the excess amount received.
2. Return the excess amount received.

Lower amount received: 

1. Presuming good faith, politely alert the counterpart that less funds have been received.
2. Indicate the missing amount.
3. Specify a payment note to receive the missing amount. If the counterpart refuses to acknowledge the missing amount, initiate a dispute and add evidence of the lower amount of payment received.