Sales invoices coming up paid by default in V18.1.22

Have just upgraded to 18.1.22 from 17.10.?. on a mac.
Anyhow when i create a sales invoice now and update it, the invoice states it is paid in full and no balance owing. This is without progressing to the receive money workflow…

any ideas how to remedy this?

make sure the customer balance is correct. maybe you have allocated extra amount in previous receive money transaction.

ok thanks for advice- the balance for this customer does seem incorrect