Provider did not accept user authorization

Hi! I have a Microsoft Live account with family members on it. One of them is a 15 years old that owns a XBOX One console and loves to play Overwatch. Now that you guys allow cross platform she wants to play with friends that own a PC.
When trying to link the Battle.net account with her console she gots the message “ Provider did not accept user authorization".

I saw the post over this subject but it is not clear if I can (as a “parent account”) change her account configuration to allow this, like disabling parent controls.

As far as could review she only has restrictions in place to buy games. All the other configurations are allowing her to do whatever she wants.

If it is a true fact maybe you could be clearer on the instructions saying that only adult accounts can play cross-platform.