Flow Designer - Save REST response as attachment failing

[Aidan]

I'm trying to utilise the "Save as attachment" option in a REST step within a flow designer action.  I've configured all of the fields (attachment name, parent document) but when run I get the following error;

Error encountered while creating Attachment. Error creating Attachment thumbnail.jpg : Method failed: (/api/now/v1/attachment/file) with code: 403 - Forbidden username/password combo

Additionally, this REST call is running via the MID server as the end point is on the local network.  It works fine if the MID server is not used and a web accessible URL is accessed.

I'm clearly missing some authentication record somewhere but for the life of me I can't work out where.

[Aidan]

Weird, my filename already ended with .txt, but at least you've got it working!

[BurtCrepeault]

I came here having had the exact same two error messages, for table sys_data_source in my case.

The write ACL on that table for the mid_server role fixed the "username/password combo" error, but the read ACL on the same table for the same role didn't work as expected. Neither did the ".txt" workaround. I'm still getting :

Error encountered while creating Attachment. Error creating Attachment manufacturers.json : JSONObject["sys_id"] not found.

I'm still looking for a cure, but would appreciate any insights you may have had since this was originally posted.

[BurtCrepeault]

Well, I finally got it. It turned out I had a business rule than yanked the attachement from the sys_data_source record before it could be read by the Flow action.