Hello,
Thanks for reaching out! I'm Microsoft user like you.
I can understand you are not able to login to Website or App.
As per Error message it looks that you are using personal or different account and which need to be added from Azure AD in which this Application hosted in tenant so that you can access using your personal account.
Kindly connect with application provider to give access of your account.
In case of additional questions, reach out back to me, and I will be happy to help and try our best to resolve your issue.
Best Regards,
Prakash