I have posted an invoice to the wrong supplier account, subsequently that invoice has been paid and the money allocated against the invoice.
The supplier is returning the monies.
How do I go about reversing the transactions. I am not using Sage, we use Redsky summit 2000
I'm not familiar with your software, but I'll give you a few suggestions.
First try going back to the invoice and changing vendors.
If you can't do that, you may have to prepare a new invoice to the correct vendor. Then try to go back to your deposit (receipt) and unapply it from the wrong invoice and apply it to the correct invoice. Then you should be able to void the incorrect invoice.
If you can't unapply/reapply the deposit, you may have to void it. Then post a new deposit, and apply the payment to the correct invoice.
Everything is usually fixable in accounting software, it's just figuring out how to get around it.
Hope that helps!