Sender telephone number: sender phone number shown in the message received by the user. This is the number that you have set up in your SMS provider account or the one that it provides you with (for example, Twilio usually does not give you the possibility to choose your number but gives you one of their choice). Usually the maximum number of characters allowed is 16.
Alphanumeric Sender ID: enter the text that should appear as the sender (this option might not work correctly in some countries, check your country with the SMS service provider you have selected). Usually the maximum number of characters allowed is 11.
Admin phone: enter here the phone numbers of the admins who will be notified via SMS. Include country calling codes. You can also specify more than one phone number. Type the number and press Enter to add a new one.