iCloud backup

I have tried backing up my iCloud account on my previous phone to enable me to access all of my photos on my new phone, but for some reason each time I click backup now it will not finish backing up (I have not only bought the 50GB of storage a month, but also left the phone to back up for 24hpurs+ & it still doesn’t)

I was wondering if you could help me back my iCloud account up. Thank you