How are you managing 4,000+ offline customer contacts on WhatsApp Business without getting flagged in India?

Looking for advice from founders who've actually solved this in India.

We run an exhibition-first Indian D2C brand and have collected around 4,000 genuine customer phone numbers over the last few years from people who've purchased from us at exhibitions. We also have details like name, city and products purchased.

We're now trying to build a proper customer communication strategy using WhatsApp Business.

Here's the situation:

We're using our primary business number (the same one printed on our bills, tags, etc.).

Recently, the account got flagged after we created a small 5-member WhatsApp group (3 family members and 2 friends, all of whom had previously chatted with the business number). No broadcasts or bulk messages had been sent.

Before we start communicating with our customer base, we want to understand the right way to do this.

A few questions for founders who've been through this:

If you're managing 3,000–10,000 customer contacts, are you using the WhatsApp Business App or the WhatsApp Business API?

How do you capture and maintain opt-in for customers collected offline?

How do you handle broadcasts and segmentation at scale?

Have you ever had your account flagged or restricted? If yes, what caused it and how did you resolve it?

Looking back, is there anything you'd set up differently from day one?

Not looking for tool recommendations or sales pitches. Just hoping to learn from people who've already solved this problem.

Thanks in advance!