Upgraded iCloud storage but remaining photos won’t sync

Hi, I have limited space on my phone so turned on iCloud for the first time. The free 5GB filled up quickly (I have 35GB of photos) so I then subscribed to the monthly 50GB allowance. However the extra photos won’t sync to iCloud and my iCloud storage still shows at 4.9GB of 50GB.

I tried turning off photos from iCloud and downloading & keeping photos back to my phone (this took some doing as I hadn’t enough storage space so had to offload most apps first to get enough free storage to do this) in order to start again from scratch with the extra storage allowance, but when I switch photos off in iCloud it says 296 (of the 400 odd) photos that were uploaded on iCloud can not be downloaded and will be deleted from my phone. No idea why. I don’t want these photos to be deleted so I cancel, and photos remains green in iCloud so I have no way of jump starting anything.

Help! Many thanks in advance.