I have the same issue for sending the fax with PDF attachment.
I create the document, attachments and sends via BCS class, but i got the following issue:
No delivery to <fax number>, as part of message cannot be transferred
Message no. XS811
Diagnosis
The message could not be delivered to recipient 6504612397 as part of the message could not be transferred.
System Response
Processing was ended normally.
Additional information of the node used (in the system language of the node):
Procedure
Part of the message could not be transported all the way to recipient <fax number>. This is usually due to particular binary attachments. Check the message and remove oversized attachments and attachments that require special coding, for example.
You should only submit an answer when you are proposing a solution to the poster's problem. If you want the poster to clarify the question or provide more information, please leave a comment instead, requesting additional details. When answering, please include specifics, such as step-by-step instructions, context for the solution, and links to useful resources. Also, please make sure that you answer complies with our Rules of Engagement.
Add a comment