Relation specified incorrectly
When a company is integrated with SortMyBooks, this error can occur if the company is not set up as a supplier/sub-contractor (Purchases) or as a customer/principle contractor (Sales).
When setting up a company in SortMyBooks, there are 4 options when setting the company up for Purchases:
SortMyBooks can only accept published purchase invoices to a company set up as either a Supplier or Sub-Contractor. To change the company setting in SortMyBooks, navigate to Supplier Settings > Financial > then change the Payee ID to Supplier or Sub-Contractor.
If you are publishing sales invoices to a customer account, the company needs to be set up as a Customer or Principal Contractor. As with a supplier, if Other is selected then SortMyBooks will not accept sales invoices.