The users do not have the correct permission set assigned to them is the most likely cause of the issue. A connected app is a framework that enables an externalapplication to integrate with Salesforce using APIs and standard protocols, such as SAML, OAuth, and OpenID Connect1. Connected apps use these protocols to authorize, authenticate, and provide single sign-on (SSO) for external apps1. To access a connected app, users must have the appropriate permissions assignedto them, either through their profile or a permission set2. If the users do not have the required permissions, they will receive an error message when they try to access the connected app. The use of high assurance sessions are required for the connected app is not a validoption, as high assurance sessions are related to multi-factor authentication (MFA), not connected apps3. The connected app setting “All users may self-authorize” is enabled is not a cause of the issue, but a possible solution. This setting allows users to access the connected app without pre-approval from an administrator4. The Salesforce administrators have revoked the OAuth authorizationis not a likely cause of the issue, as OAuth authorization is granted by the users, not the administrators5. Revoking OAuth authorization would also affect all users, not just a group of them.