Auto Invoicing for non VAT Sellers

We received an Invoice Defect Rate warning as it’s 50%. We hardly get any business sales and I monitor them manually, and out of the 2 we’ve had 1 of them I was late with uploading the invoice (as the order was in Pending for several days).

We’re not VAT registered, so don’t think we can use the Amazon Auto Service.

How do people normally handle this - is there a paid service anyone could recommend, or even an email alert for Business orders beings shipped so that I would know to upload an invoice?

TIA