WhatsApp knows that it's uncommon for someone to send so many messages or bulk messages to people they've never talked to each other before so it considers as spam/marketing junk pretty fast. There is some tips before sending message to WhatsApp.
Dos and Don'ts:
Have in mind:
As API provider we say all that's left to do right now is agreeing with WhatsApp's policy, not sending spam messages and always wait for the other person to contact you first. You could make it by sending an SMS to the person with a link to start a chat on WhatsApp with you.