I found this search, it appears it may be Google issue:
https://www.reddit.com/r/GooglePixel/comments/176mn8g/bmw_digital_key/
Edit: It appears there is a pairing process that uses the G Wallet. It is also say many users have issues with this “pairing”. I would try with the alternate wallet that Gael suggested:
Keep searching, looks hopeful there may be a solution… 