Hi @Pauline Janssens ,
Welcome to our forum!
What's your account? An Outlook.com account or anything else?
In order to further confirm if the issue is related to Outlook for Mac, it's suggested that you could log in to you web mail to check if there're any differences.
On the other hand, please add another account in Outlook for Mac to check if the issue persists.
Based on my research on "Error Tag: 9hehw", i found that the error my occur on mobile device and be related to authenticator, if you are using authenticator, it's suggested that you could check your authenticator.
Hope to help you!
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