What to do when you get "Authentication failed" error while sending emails or invoices
TL;DR: The "Authentication failed" error means your Microsoft or Google email token has expired. Reconnect your email account in Settings to resolve it.
Who can do this
Any Uku user with a connected Microsoft or Google email account
Users on the Team or Enterprise plan with email sending enabled
Why does this happen?
This error occurs when your Microsoft or Google account token has expired. A token is a temporary security code that allows Uku to send emails on your behalf. Tokens need to be refreshed periodically, and when they expire, Uku can no longer authenticate with your email provider.
How to reconnect your email account
Open Settings.
Select Emails.
Select Email addresses.
Locate your email account (it will be highlighted in pink to indicate a connection issue).
Select that email account.
Select Reconnect.
After reconnecting, email sending should work again.
Resending failed emails
If email sending failed while your account was disconnected, you can resend those emails. Read here how to resend emails that failed to deliver.
Tip: If you frequently encounter this error, check whether your organization's security policies are causing tokens to expire sooner than expected. Your IT administrator may need to adjust token lifetime settings.
Troubleshooting
Reconnect button does not appear: Make sure you are viewing the correct email account entry. If the account is not highlighted in pink, the issue may be different from an expired token.
Error persists after reconnecting: Sign out of your Microsoft or Google account in your browser, then try the reconnect process again. This forces a fresh authentication.
Multiple email accounts affected: If all connected email accounts show the error simultaneously, check whether your organization recently changed security policies or revoked third-party app permissions.
Invoices still failing after reconnection: Verify that your email account is set as the default sender for invoices under Settings > Emails > Email addresses.