If you used Azure DevOps long enough, you will eventually run into a situation like this - your Service Principal will expire and throw this error:
Don’t panic if you see this - when you authorise an Azure Resource Manager Service Connection Azure DevOps creates a new App Registration in Azure Active Directory (even if you are using as public tenant like hotmail - you will still get an AAD tenant to use):
This App Registration has a default expiration of two years:
The error simply means that your Service Principal expired. All you have to do is to renew the Service Principal from the Azure DevOps UI and you will be good to go. Don’t renew it from the Portal, as otherwise Azure DevOps won’t know how to handle the secret!