Where and how can i enable Deployment concurrency control

[John de Villa]

Where and how can i enable Deployment concurrency control. We want to 

ensure only one deployment runs at a time per environment.

[Aron Gombas _Midori_]

I think all you need to do is setting the "deployment" field on your "step", then Bitbucket Pipelines will guarantee that only one step with a given deployment can run at a time. (The earliest will run, others will stop in "Halted" state.)

On the UI, it looks like this: https://support.atlassian.com/bitbucket-cloud/docs/deployment-concurrency-control/