"Please enter a valid email address" does not always mean that the email address is really invalid because in some instances we may not have recognized the domain but I would suggest that you double-check.

We use email-validation services that ping the actual email addresses. This is both to help our users in the case of a typo as well as protect users from spam-related email addresses. Though, if it is an email address with custom hosting or a less popular provider, in some rare occasions our validation may think it is invalid because their host was temporarily unavailable or the email check bounced at some point.

If you are certain that your client’s email address is correct, feel free to contact us and we will quickly resolve the problem by whitelisting the email address.
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