it won’t let me buy more storage no matter what i do

You cannot buy more storage for the phone. It will always have the same amount of storage it came with. You can buy space in iCloud, Apple's syncing service. To create more space you must remove photos, messages, apps, etc. Check these links...

https://support.apple.com/en-us/HT20165

Clear Other storage on your iPhone or iPad - Apple Support

If you are on the iOS 14 beta version, we cannot help you here.

Since buying iCloud storage has nothing to do with the beta it is OK to answer the question, or your can suggest they roll out of the beta and provide the link to do so, or you can suggest that they report the problem to Apple with the Feedback tool they got when they installed the Beta. All are OK.

You're welcome, it would have been nice if the OP had written a better question such as saying when I try to update my iCloud storage it says, ______________ which would have indicated whether it was a message from Apple's server, such as a payment issue. That would have nothing to do with the beta.

Thanks kb, I didn't notice the iOS 14.

No problem. I have missed small things in some of my posts to people too. I just read too fast and then answer what I think is the question.

Thanks for that clarification.