Hello @NixC, I'd be more than happy to help look into this with you.
I'll just need a bit more info to make sure that I have a better understanding of your concern. For example:
Are you having an issue adding any sort of photo or specific ones? Any photos and now I know any files too.
Have you tried uploading these photos after connecting to a different WiFi network or via cellular data? Yes have tried on different Wifi networks and cellular data
How much space have you got left on your mobile's storage in general? 200 GB available on phone and 3 TB free on Dropbox.
A screenshot (without any personal details) of the error message would also be very helpful.
Looking forward to hearing back from you!
Thanks for helping out with this - I had planned to use Dropbox predominantly to quickly transfer photos from my phone (apple) t omy desktop (Windows) without using iCloud. At the moment that function isn't working.