Adding a guest user error message: The user(s) below are not eligible for guest accounts

I own a Community that allows guest users. Most users I add are fine but, I add one person and I get the error message: The user(s) below are not eligible for guest accounts. Click on the question mark icon next to each user's email for more details.

I do not know why. Is it the format of their email address: xxx.xxx@xxx-x.com. Is it because of the dash in the domain name?

Thanks

It should not be an issue with the dash in the domain for this guest user. I assume that this is for Connections cloud environment and not on-Prem. Please open a case with HCL Support so that we can look into the account specifically. Typically when this has been reported, it is indicative of a possible issue with the user account.

It's likely that the one user you are trying to add already has a guest house account that needs to be cleared. HCL support can definitely assist with that.