Check -> Go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB or 2 TB) then you have an iCloud subscription.
If you have an iCloud subscription, you will receive a monthly bill from Apple, check your email box.
You pay monthly for iCloud storage.
If you have upgraded iCloud storage, it would take about 1 to 3 business days in order to process.
Once your request for iCloud+ has been activated, you should receive an invoice in your email box.
See -> Access and view iCloud Photos on your iPhone, iPad or iPod touch
Access and view iCloud Photos on your iPhone, iPad or iPod touch – Apple Support (UK)
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Do more with your photos
See also -> Manage your iCloud storage
Manage your iCloud storage - Apple Support