Before getting into the best first message format for not getting blocked, let us understand why a number gets banned.
If multiple people report your number as spam back-to-back (in quick succession) then WhatsApp will ban your number.
Check this article to see all the different reasons why the WhatsApp number gets banned.
When you send the first messages to unknown numbers, they get three options on their WhatsApp screen.

And if they click report or block, that’s where you’ll fall into trouble.
But if they send you at least one reply then they see this,

Now the chances of blocking are less, as you see the “Report” option is gone and now reporting is 2 steps instead of just 1.

And if they save your number, the blocking rate becomes even lower.

And once they have replied the more you chat, the block button becomes hidden so the chances of blocking/reporting become even lower.

Hence, it is very important that your first message has to be crafted in such a way that they send you a reply instead of clicking on block or report spam.
So how to do that?
How to make sure that they reply to your first message instead of blocking/reporting you?
1️⃣ In the first message, share a relevant update.
2️⃣ Phrase it like a question, so they will give an answer.
3️⃣ Give them an option to opt out.

WASender Bulk Messaging Best Practices
1️⃣ Start with sharing an update.
2️⃣ Don’t send a link in the first message (They won’t be able to click on that link).
3️⃣ Give them an option to opt out.
4️⃣ Send the link only after they have replied to your message at least once.
5️⃣ If they agree to receive updates, ask them to save your number.
6️⃣ Share 90% valuable content and 10% promotion (Not the other way around).
7️⃣ Use WhatsApp status to remain familiar with your contacts.

Yes
GOOD INPUTS