Appreciate the update, @Torquil.

I'll share details about how your application works in QuickBooks Online (QBO).

The applications in QBO decide how the information is shared through the integration. It is not primarily a third-party issue since we can't view how the app works with the system.

Therefore, it's best to contact the Technical Support of Integromat and let one of their specialists know about how the messages for your customers on invoices are missing.

You may also read this article for the steps in creating a document showing what comes overdue for your customer's sales activity with you: Send Invoice Reminders Automatically or Manually in QuickBooks Online.

If there's anything else that I can help you with aside from working with your apps in QBO, please let me know by leaving a comment below. I'll be here to lend a helping hand. Take care always!