Referee Phone error: This field can only be a valid phone number, with extension in "-extension" format

Hi All,
I am submitting my application and on the page where I have to submit the phone number of a referee (author of recommendation letter) it asks for their phone number.
No matter how I enter the phone number with “+” or without it, with “()” or without it, it always gives me the following error:

  • +447777123456 : This field can only be a valid phone number, with extension in “-extension” format.

Did anyone have the same problem? Do you know how to solve it ?
I am entering 2 UK numbers and one Cayman Islands number.

Thank you in advance!

Try 0044 and number. Use extension prefix field. I t should be ok.