App Store Sign in/Purchase problems

On my MacBook Pro which is running MacOS Mojave version 10.14.3 I have 222+ gb of storage.

Whenever I open the App Store at the bottom left it says Sign in. Once I type in my username and password which is without a doubt correct I hit Sign in and nothing happens at all. It still gives me the sign in option in the same corner after. (My store is up to date also)

I try doing this because I want to Purchase AFFINITY PHOTO. (Yes I have enough money on my credit card and apple has the correct billing info) I get an error every time (see bottom). I'm using Hotspot with my iPhone for an internet connection via sprint service. I'm starting to think maybe it's my internet speeds but at the same time I don't think my speeds have anything to do with not being able to sign into the store because I can do pretty much anything on this Mac and I've done my last software update with hotspot wifi as well.. Here's my error. Iv'e tried restarting my Mac, I obviously tried signing out of the App Store but it won't even let me sign in. I disconnected from my hotspot and waited a while to reconnect. I even tried doing this at my job so I don't think its a location problem. Some help would be obliged. Thanks