You can send from 1,000 to 100,000 messages per day.
There are three levels of restrictions, according to the WhatsApp documentation:
Level 1: Allows your company to send messages up to 1,000 unique contacts within 24 hours.
Level 2: Allows your company to send messages up to 10,000 unique contacts within 24 hours.
Level 3. Allows your company to send messages up to 100,000 unique contacts within 24 hours.
When registering, the phone number always has level 1