iPhone setup issue - company portal issue

Hi

I have a user who cannot set their phone up. It's all been provisioned ok, but the user cannot set their iPhone up. When they sign into the company portal on the iPhone, it says their credentials are incorrect. She is using her company e-mail address and password, and we know her credentials are ok, as we've tested them signing into her Microsoft account. But company portal on her iphone keeps saying her credentials are incorrect.

Can anyone offer any advice?

Many thanks

Andy