Why I'm not able to login my outlook account in mail app in iPhone

I want to open my email

My problem is similar to yours. I have contracted Microsoft365 for the administration and management of our company's emails. Something curious happens to me with two email accounts in only 2 of the 8 Apple devices we have in the company. The rest of the devices have Linux, Windows and Android operating systems. The 2 devices in question have the following infrastructure:
iPhone Xr, iOS 18.3.2 version.
iPhone 13, iOS 18.3.1 version.

When trying to authenticate with the username and password on each of these devices, both for the Outlook app and the Teams app, we get the following error: “AADST50020: User account from identity provider does not exist in tenant ‘domain.com’ and cannot access the application (Outlook Mobile / Teams Mobile) in that tenant. The account needs to be added as an external user in the tenant first. Sign out and sign in again with a different Azure Active Directory user account.”
The users exist, are active and have all the appropriate permissions just like the rest of the 16 accounts we have contracted.
Does anyone know how to fix this issue. Microsoft replied that because Apple is a third party, their support is limited and they cannot help me.

I found a way to access Outlook on your Iphone.

Open your phone's browser and sign in to Office 365, then access Outlook. Once your emails are displayed, tap the share option and scroll down until you see "Add to Home Screen." This will create a shortcut to the browser version right on your home screen.

Try adding your account to outlook on a desktop first. Then try to add to the outlook app on your phone. This worked for me this morning finally.

Except that even in the app, Microsoft isn't seeing my account. So I really do need to talk to someone in Microsoft tech support and it's very frustrating that there is no one to talk to.