Thank you for your response, the import is now working.

You assumed correctly that it is an import into the Ledger not Receivables. As a non-profit/charity we don't have many Receivables but we do have many donations to process in our database, so we don't even have the Receivables module.

I went back to check defaults and put in a filler as you suggested for the entry number for 6 and changed that field to the default 6. The fiscal period default is 6, I don't know why, but it worked with that.