Make "external" stage run only when the stages before it have completed successfully

I have a project which is connected to Terraform Cloud. Each time there is a change in the repo code, it triggers a Terraform plan on Terraform Cloud.

In my file, I have a stage called validate which runs to verify that the terraform code is up to standard. What I want to do is that the external terraform job should only run when the validate stage has completed successfully.

I have tried a magnitude of keywords (trigger, only, needs) but nothing can control the external stage. It has no dependency on anything so it always runs. At the same time as the first job.

How do I make it run after my first stage has completed?