Can no longer make App Store purchases

I've recently both Federated our domain, and set it as the domain for managed Apple IDs, and I'm guessing this is somehow related to that, but I can no longer update/purchase apps through the App Store. I get the following pop up.

For the life of me I can't figure out where or how to change any settings to allow this. I'm assuming this is related to our settings in ABM, because as far as I can recall, there's nothing in our MDM (Mosyle) that would impact that.

Specifically, I already have the app installed, but the trial version has expired and I'm looking to 'upgrade' it to a purchased copy, which I can't do, because it has to be done through the App Store.

I've tried a workaround by 'purchasing' the app through VPP and installing it by our MDM, but it just gives me an error. It also shows as a $0 purchase, so I imagine I would face the same issue trying to upgrade it to the full version.

Any suggestions would be appreciated.

[Edited by Moderator]