Josh,
The Error message points to an Account Type entered where that Type has the GST Bus. Posting Group setup or populated (i.e. G/L Account, Customer, Vendor, Bank). Now if you are not using a Customer, Vendor or Bank on your G/L Journal Line, what does the Chart of Accounts, for the Account No. you are using, show for the GST Bus. Posting Group? Here is my page as an example:

I am guessing your are posting a payment and you will hit the Bank Account, which should not have GST Bus. Posting Group, the GL Account related to the Bank Posting Group should not have one setup either. The Customer does have one setup but the G/L Account for Accounts Receivable will not have one setup so it will be OK. Maybe send a screen shot of the entry to help assist if you cannot resolve.
Hope this helps.
Thanks,
Steve