Hello @MarshfieldCC
If you’re setting the nominal on the sales invoice, it should set all OK. The only time this may change is if you then select an item (the first column on the invoice lines) after selecting a different nominal.
Do you have mixed items on your invoices? If so, the quickest way to resolve this would be to just journal it to the correct code. If you have individual invoices, you can bulk recode them, but you would need to know what invoices they are.
These posts may help: