I’ve still made no progress with this. I would be interested to hear from anyone who has had success uploading to Digital Ocean - using the multiple file option - to help point me in the right direction.
Patrick suggested the credentials might be incorrect, which would seem the most likely cause. However, given I have no problem using uploading a single file, using the same server action, I would have thought the credentials must be correct.
I would be very grateful for any suggestions. I would really like to be able to use this feature.