The vendor coded to the invoice doesn't exist in Rent Manager anymore.
It's possible that someone deleted the vendor in Rent Manager. If a vendor is deleted in Rent Manager that deletion cannot be communicated back to Beanworks. So the vendor would stay active in Beanworks and create possible sync error such as this one.
We advise to make your vendors inactive if possible. When you make vendors inactive in Rent Manager and a sync occurs then the vendor will be inactive in Beanworks too. This means you can no longer coded invoices use that vendor in our system.
Although if you have still have invoices which are currently going through the workflow in Beanworks such as invoices in the following statuses N, IP, R, RE, PA, A coded with that (inactive) vendor. Then those invoices will still sync into Rent Manager when exported from Beanworks.