Hello. I recently heard from a repeat customer that there was an error on my payment page when filling in his contact information. No problems have ever occurred for my store before today, but after completing the field box for "Email or mobile phone number" with both his email address and then his phone number he continued to see an error message at the bottom of the page "please enter a valid phone number". After multiple tries my customer was unable to complete payment for his order. Please help. I have attached a screen shot of the issue and error message if that helps. Thank you.
The issue is that a shipping address phone number is not entered. It is the bottom field in the screenshot you provided (which is blank in the picture). You can set it in your checkout settings for this field to be required, optional, or hidden at check for your customers.
In your admin go to Settings -> Checkout Settings, and look for the section pictured below.