A WhatsApp broadcast is not an email newsletter pasted into a chat. People open it next to messages from friends, so the first line has to earn the rest.
Lead with one offer or one update. Name who it is for. End with a reply they can send in a few words, such as YES, STOP, or a size.
Send only to contacts who opted in, and use an approved template. Then read the replies in the shared inbox instead of treating the send as the end of the job.