All WhatsApp Business API accounts are based on a valid phone number. The following rules apply: 

• You must own this number and be able to access it during the time your channel is active.
• The number must include a country code and an area code.
• If it is a voice-only capable number, or a landline, it must be able to receive international calls.
• The number must be able to receive international calls or SMS for the channel activation.
• The number needs to be 'clean', which means it mustn't have been registered with another WhatsApp user. If you are using a number for the WhatsApp App and would like to use this in the API, it is possible to migrate the number. Please follow the steps in WhatsApp phone number: From mobile app to API

These types of numbers are accepted:

• Landline numbers that accept international calls
• Mobile numbers
• Virtual Mobile Numbers (VMN); Need to be voice-capable to receive the activation token by call. VMNs can be purchased from MessageBird.

These types of numbers are not accepted: 

• Shortcodes
• Numbers with an IVR (automated call menu) attached to it, unless this can be disabled to receive the activation token.
• Toll-free numbers
• Voice capable numbers unable to receive international calls
• Voice capable numbers that require extra zeros or digits apart from the international number format. A phone number in full international format includes a plus sign (+) followed by the country code, city code, and local phone number.

Note  If you have switched from the WhatsApp Business App to the API using the same number and are now looking to switch back, please review WhatsApp phone number: From mobile app to API