Settingup External Users to Test my App

Hi I'm trying to setup external users to test my app. When I get to the screen attached its not letting me complete the setup because it says I have to only use numbers for the phone number. I have only used numbers, I've ensure I've done so but its not recognizing this. Has anyone else had this issue? Could you make suggestions as to how to fix the problem?

[Image Edited by Moderator to Remove Personal Information]

Settingup External Users to Test my App
 
 
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