Why WhatsApp is different
Reach on WhatsApp is not a follower count. It is a member count times the number of groups those members forward into. A society group of 300, a deal group of 800, a batch group of 60 that forwards into ten hostel groups: the audience is dense, local and trusted, and it has never been measurable. Ad platforms cannot enter it; networks report on it weeks later in aggregate.
For brands: reach groups through their admins
You do not message groups; their admins do. Publish an offer with a reward per order or sign-up and a ready-made message; admins take it and post with their own link. Each group's opens, cities and results show up separately, so you learn which groups buy and which only forward. Pay the admin per counted result, from the budget you locked, and they will post your Friday special instead of somebody else's.
A reward per order is small and the volume is high; ₹40 to ₹80 per first order is common thinking for food and grocery, more for higher tickets. The floor for your ticket size is the least you should offer.
For admins: a link per group, a message that fits
Sign in with a code on WhatsApp. Make one link per group or broadcast list, so you can see which group acts. Use the ready-made message or your own words, say it is a referral link, and post the offer once — not five times a day. Groups that trust you buy more; groups that mute you buy nothing.
Reading the numbers
Opens attributed to WhatsApp, with the city, tell you the message is being read. A forwarding estimate tells you it travelled beyond your group. Second visits tell you a group liked what it found. Results per group tell you where to post next week. All of it is live, and the brand sees the same for your link.
What not to do
Do not add people to groups without consent, broadcast to lists that did not opt in, or run a referral on top of a coupon on top of a platform discount until the numbers mean nothing. Do not reward opens: they are forwarded for fun. Do not buy traffic: results from it are reversed and the account follows.
One week, concretely
A kitchen publishes 'Friday menu — ₹60 per first order, society link gives free delivery' with a ₹6,000 budget. Ten society admins take it. Friday evening: 900 opens, 110 first orders, ₹6,600 paid to admins, ₹990 in fees, the campaign paused itself at the budget and the kitchen topped up. The illustrative numbers are made up; the shape of the week is not.