One of my users can't sign in to Teams with error AADSTS50020

Hello @BF Admin

From what you described, only one user is experiencing a sign‑in issue when accessing Microsoft Teams on an iPhone, and the sign‑in fails with the error AADSTS50020.

About the error AADSTS50020, it usually means that the user account being used is not recognized in the tenant they are trying to sign in to, or the account is trying to authenticate against the wrong Microsoft Entra ID (Azure AD) organization.

In general, this happens when:

• The email address exists in more than one Microsoft tenant
• The account was added as a guest but is signing in incorrectly
• There is a conflict with cached credentials, especially on mobile devices

*To address the issue better, it would help to clarify:

• Is the affected user a guest user or an internal user?
• Does this same user successfully sign in via Teams on web or desktop, or does the issue only occur on iPhone?
• Has the user been invited to multiple Microsoft organizations?

These answers help determine whether the issue is identity‑related or device‑specific.

Besides, I suggest that you can try these following troubleshooting steps in order to see if it helps

1/ Clear the Teams App Cache

• Open Teams on your iPhone/iPad.
• Tap your profile picture (top left) and go to "Settings".
• Select "Data and storage".
• Tap "Clear app data".
• Restart the iPhone before trying to sign in again.

2/ The deeper clean

If step 1 fails, do this:

• Sign out of all Microsoft Apps on the iPhone (Outlook, OneDrive, Word).
• Uninstall the Teams app.
• Go to "Settings" > "General" > "VPN & Device Management". Remove any "Work or School" profiles if they shouldn't be there.
• Clear Safari Cache: "Settings" > "Safari" > "Clear History and Website Data".
• Reinstall Teams from the App Store.
• When prompted to sign in, manually type the email address instead of selecting a suggested one.

3/ Verify correct account type

• When prompted, choose Work or school account
• Avoid using any saved personal Microsoft account

5/ Try Teams on the web

• Ask the user to sign in via teams.microsoft.com in private mode (Ctr+ Shift + N) using the same email

If you still need my assistance, please come back with screenshots or any additional details so I can review it again and see if there’s anything more I can help you with.  

Have a nice day!

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Error AADSTS50020 indicates that the account being used on the iPhone does not exist in the target Microsoft Entra (Azure AD) tenant or does not have access to the Teams application in that tenant.

Troubleshoot in this order:

1. Confirm the correct account and tenant
   • Check the full error text for User account and Identity provider values and verify they match the account and tenant that should have access.
   • Common issue: the user is signed in with a personal Microsoft account (Outlook/Hotmail/live.com) instead of the work/school account, or with the wrong organization account.
2. Sign out and clear cached sessions on the iPhone
   • In the Teams mobile app, sign out of all accounts.
   • Close Teams completely.
   • Open Safari (or the default browser), go to any Microsoft sign-in page, and sign out there as well.
   • On the iPhone, open a private/incognito tab and sign in again to Teams using the correct work/school account and tenant.
3. Check if the user is a guest and has been invited
   • If the user is trying to access another organization’s Teams as a guest, ensure that organization has explicitly invited the user as a guest in its Microsoft Entra tenant.
   • The external organization’s admin must:
     • Go to Microsoft Entra ID → Users → New guest user and invite the user’s email.
     • The user must accept the invitation email before trying Teams again.
4. Verify app registration / access requirements (admin)
   • If Teams or a related enterprise app is configured to require user assignment, ensure the affected user (or a group they belong to) is assigned to the application in Enterprise applications → [App] → Users and groups.
5. Validate sign-in audience and endpoints (for custom apps using Entra auth)
   • If the error appears when accessing a custom app that integrates with Teams and Entra ID, confirm:
     • The app registration is not single-tenant if users from other tenants or personal accounts must sign in.
     • The app uses the correct authority URL (/organizations, /common, or /consumers) based on the configured signInAudience.

If, after these checks, the user still cannot sign in, review Entra sign-in logs for that user to confirm whether they are hitting the wrong tenant, missing guest invitation, or blocked by assignment requirements.

References:

• Error AADSTS50020 - User account from identity provider does not exist in tenant
• Error AADSTS50020 when signing in to the OneDrive sync app
• Why am I having trouble signing in to Microsoft Teams?