After you have saved the billing document, the following message appears in the status bar:
Document 90036111 saved (no accounting document generated).
What are the possible reasons why no accounting document has been created? (Choose two) 

A posting block was set for the billing document type. This prevents the creation of the FI accounting documents. However, controlling documents were generated.

The reference number and assignment number differ. Therefore, accounting documents cannot be generated. 

In the billing type used, there is a configured posting block. Therefore, the blocked billing document has to be released. 

The account determination cannot determine an account, or determines an account that cannot be posted to automatically.