When sending messages via the 360dialog WhatsApp API, you cannot use a phone number as recipient. Facebook requires to look up the wa_id , which is used as the only valid destination identifier, for each phone number you want to send a message.
At this step you will also receive the information, whether the phone number has a valid WhatsApp account or not.
Only wa_id's with statusvalid can receive messages.
If you receive ‘processing’ status, use blocking=wait param? The request will take longer but result will be ‘valid’ or ‘invalid.
An "invalid" Phone Number can become "valid" through correct formatting. Please make sure you follow Formatting Guidelines.