An attachment has its own requirements: the supported media type and size, a readable file, and the selected API's upload or URL contract. A successful text send does not confirm that the media was fetched or uploaded correctly.
Check the attachment error and the file's accessibility without publishing a private customer file. Use a harmless test file to separate a media problem from a connection problem. Report the file type, size, time, and redacted error to support. Remove signed download links, storage credentials, and unrelated personal information from logs.