same board with client separate teams

Hi,

We have a bit of problem with integration with a client.
They are using Monday, we are using Monday.

Our company would like to duplicate board
( Cross account copier) we have tried this. But problem is we need the board to update if they do, same we want our ‘client’ to be able to approve and it will replica on their board.

There should be no access from either on each board as it is not same teams at all.

Many thanks,
Elin