shared sheet not giving access to shared with user

I have shared a sheet with a new colleague, they are getting the email invite, but when clicking the sheet link, its saying they don't have access and to contact the owner. However, when I look on the user list, they are on the list. They don't have a licence, but don't need one as just a user with viewer access rights. I have never had this problem before, can anyone advise? thanks

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