The only numbers that cannot be used as an endpoint are special services such as Emergency Services (Police, Fire, Ambulance), premium rate services (hotlines), network services (directories) and network and carrier services.
The format for an endpoint is dependent on the country of the phone number. If the endpoint is a United States mobile phone number, simply enter the phone number and the number will automatically format. For example, if the endpoint is ‘555-0123’, the validation will update the number to ‘+1 201 555 0123’ once you have confirmed the step. You do not need to include any symbols or spacing when entering the endpoint.