When you add it to your DJI account it tells you it is already bound to another account? If so it would not be possible to bind it. Are you using the account from the previous owner?
Binding is confusing; there are a couple of methods and it's not always obvious and straightforward. This might help:
How to rebind a used DJI drone: Step-by-step guide
It really. When I log into my own account and connect to the drone, in the device management, it shows the drone as bound to another account and I’m unable to unbind it from said account or bind it to mine. However, there are none of the...
So I bought an Air 3 that the previous owner had been having issues unbinding. For whatever reason, it’s showing in their app as removed from their account but on my end, still shows as bound. However, there are no restrictions and I’m able to...