When you're trying to apply for Facebook Permissions for your application, you may encounter some permissions that requires App Review. In my case, I need to use the Facebook Login for Business Accounts, so I need to apply for Facebook's App Review.
In order to make an App Review for Facebook, you will need to provide step-by-steps videos and guides for Facebook testers to test for themselves. However, it does requires a Test User to do this.
A Test User can have a Test Page linked to it, and a Test Page is capable to link an Instagram Account created using this Test User. However, for some reason, I'm not able to convert this created Instagram Account as a Business Instagram Account using the Test User. I tried to link it using my application flow, but the "Convert to Business Profile" button does nothing, and if I try to do this in the Facebook Test Page account, the form that ask for Contact Information always throws a message "An Error Ocurred".
So, I'm unable to create an Instagram Business for testing and also not allowed to provide a real account because they don't allow this, as they explicitly says (Which I can agree with):
Note: Do not provide your personal Facebook account credentials.
As I'm unable to find a way around this, and I can't see to find any answer on the internet... I wonder if somebody could help with this one.
So, it seems it's just a Facebook bug (Just as one I was experiencing before this one, where after updating a Test Account permissions, the permissions were still not working properly) where the Test Account seems to be kind of locked in a state were you can basically do nothing more with it than what you have already done... So I end up creating a new Test Account and doing the same process, but this time it worked.