The number you entered is not eligible to be transferred to Inbox. Note if you have a WhatsApp Messenger account or a WhatsApp Business account that’s active in group chats, you won’t be eligible to transfer your account to Inbox. Learn more.
This is the error I was getting from Meta Business Suite when I was trying to link WhatsApp in its dashboard.

In this above photo, you see I added my account. You can message me on Whatsapp by clicking here for help too. Free HELP. 🙂
I was looking for a solution and got a solution. Even I mentioned in Reddit that I didn’t find any solution and I lost all of my customer data. See:

But later I found a solution.
So what I did do?
1) I created an account in WhatsApp Messenger and then deleted it from the app by clicking “delete my account”. You will find it in the settings.
2) Then again I created a Business Whatsapp account from the WA Business Mobile app and deleted it in the same way.
3) Then I came to Facebook, I had 3 FB profiles where I added that Whatsapp number. I went to each profile and removed that WhatsApp number from the “linked accounts” section on Facebook.

4) Then I waited for 5 minutes. And again I visited Meta Business Suite.
And done, It really worked. I am happy. Message me for free help https://wa.me/8801617972170
Hope this will help someone. 🙂
Thank you.