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 is considered spam/marketing junk pretty fast. There are some tips before sending a message to WhatsApp
As API providers we say all that's left to do right now is agree with WhatsApp's policy, not send 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.