Build create not working without build number

I can’t trigger a new build using the API without informing a build number. Reading the docs and GitHub ticket related to this feature, made me understand that I don’t need any per-existent data to start a new build.

But when I try to run the command, I get the following error:

Can someone help me figuring out what’s wrong?

My environment:
Drone 1.9 running on Kubernetes
Bitbucket server (Stash) v.5.16.11