Symptoms
This has been going on for days, but I'm getting a "We received a bad request"
Diagnoses
While on call with customer it was discovered that the environment wasn't allowing for the ability to Appify any lists/ libraries for that user and others.
Resolution
Support had the customer log in to the environments global admin account. We proceeded to run the registration wizard, along with trying to Appify a list and it was discovered that running the registration wizard did fix the issue.