Error: application checkCustomerExists fails
Check if you have a connection with your application: 
Do the following checks:
1. We can only match the e-mailadres to one debtor. Does the email address appear several times in the ERP system? It must be unique on 1 customer.
2. Is the debtor active? In other words not blocked.
3. In cause you setup a default debtor in your settings, check is the e-mailadres and debtor ID you field in, is correct. Integration > orderflow > settings > customer settings 