How to Resolve Duplicate Username Errors When Logging in with SSO (Single Sign-On) in Salesforce

Follow the steps below to identify and resolve the duplicate username error. There are two common causes: a duplicate username in Salesforce, or a misconfigured Federation ID. Work through both sections if the issue persists after the first.

Step 1: Check for Duplicate Usernames

1. Go to Setup (click the gear icon in the top right, then select Setup).

2. In the Quick Find box, type Users and select Users under Administer.

3. Find the user experiencing the issue. Search by username or email address.

4. Check the Username field for the user.

5. If the username is duplicated, change it to a unique value. Salesforce usernames must be unique across all Salesforce organizations globally.

6. If the duplicate username is intentional (for example, the same person has accounts in multiple orgs), ensure your SSO configuration maps users by their unique Salesforce User ID or Federation ID — not by username alone.

Step 2: Review Federation ID and SSO Configuration

1. In Setup, type Single Sign-On Settings in the Quick Find box and select it.

2. Review the Federation ID for the affected user. The Federation ID in Salesforce must exactly match the unique identifier your Identity Provider (IdP) sends during the SAML assertion.

3. Confirm that your Identity Provider is sending the correct and unique identifier for this user. Contact your IdP administrator if you are unsure which attribute is being sent.

4. If you update the Federation ID in Salesforce, ask the user to attempt login again.

5. If the issue persists, review the SSO login history for more detail on the error. In Setup, type Login History in the Quick Find box and select it. Filter by the affected user to identify the specific failure reason.