Currently part of the Text-to-Give process is expecting the donor mobile number to be in the format of
[+] [country code] [subscriber number including area code]
otherwise it will break with an Outgoing API error with the API Endpoint /2010-04-01/Accounts/{AccountSid}/Messages.
For example, the telephone number for the Museum of Copenhagen in Denmark is 33210772. That number would be formatted as +45-33210772 which would be 2 numbers short, and would generate the same error above.