Error message: Sorry, something went wrong during the file upload...

MacPro 2016 - OS 12.6.8. Safari Version 16.6 (17615.3.12.11.3, 17615)
Scheduled some posts last week that went earlier today, but the posted video is not playing on any of the social platforms. Went back into Express just now and the video plays fine in Express main preview before attempting to post. But once I begin to post to social media, the video file just won't upload and I get the following message: "Sorry, something went wrong during the file upload. Please try again in a few minutes."
I have tried again and again over the last 30 mins without success.
I have tried to post a previously successfully posted video, and it has the same problem.
Really dispappointed that Express seems to have these intermittent faults that seriously inhibit one's faith in posting to social media consistently and on time.