Converting Imported Invoices to Sage Invoices

We've very recently migrated to Business Cloud Accounting and wanted to make use of some 3rd party software (Chaser) to manage our credit control.

We generate all sales invoices via our job tracking software and simply use Quick Entries via an excel spreadsheet.

The credit control software we wanted to use will not gather any information from invoices that are not generated via Sage, so cannot 'see' any transactions. Is there a work-around for this? Or has anybody got other recommendations on how we auto-generate credit control letters based on days overdue?