You are getting the OAuth connection error or a 401 web page error is displayed when integrating Azure DevOps.
These issues are related to the security settings in your Azure DevOps portal where certain security policies are rejecting connections to Git Integration for Jira app.
On most cases, this is caused by an OAuth setting being turned OFF.
Git Integration for Jira Cloud requires Git admins to allow the third-party app access OAuth security policy in their organization settings:
On your VSTS/Azure DevOps portal, go to the home page.
Click an organization then go to Organization Settings (sidebar).
Under Security, click Policies.
Ensure that the Third-party application access via OAuth option is set to ON.