Hello Ismael,
There can be various reason why system was unable to generate FI documents upon saving of SD billing document few common once are below:
1. Incorrect posting period
2. Incorrect account determination etc.
Coming back to your post, your question is not clear, can you please explain what exactly do you want.
Just a guess:
1. Do you want to block generation of accounting document when you create a billing document, if so then add a posting block in billing document type "VOFA" and you can later manually release billing document to accounting using VF02.
Or
2. You mean to say, you want to create accounting document for the billing document which had an error: in this case you need to correct the issue due to which system was unable to generate FI documents and manually release billing document to accounting using VF02.
If your getting any specific error please post it here so that we can understand the issue better.
Regards,
Naveen K.