Error: "oauth2 authorisation code was already redeemed" - any ideas?

[Metworks_IT]

Hello,
One of our users is trying to sign in with his work Microsoft account, we get this error “oauth2 authorisation code was already redeemed”

All other users seem to be signing in OK.
The account is linked to AzureAD.
Tried on different devices (laptop/mobile), same error.
Any ideas how to sort it?

Thanks,
Gabriel