These are the things you should check first:
1) That the supplier is in the supplier list in Compello.
2) Both of the two key fields (usually bank account and VAT number) are correctly registered.
3) Neither of the two key fields are duplicated elsewhere in the supplier list for the client.
3) The key fields in he suplier list match what is actually on the invoice.
4) The key field data on the invoice is legible (for "OCR" invoices)
If all of thises are correct, send a message to support@compello.com and give us the supplier, client and archive number of the invoice.