If your workflow fails to run and create jobs, and has the status "NEEDS SETUP" in the Workflows page, along with the below error message:
We weren't able to start this workflow.
Encountered errors trying to create workflows from this config: Unsupported or missing workflows config version
For more examples see the Workflows documentation.
The likely cause for this is that version 2.1 was specified in the config.yml but `Enable build processing (preview)` was not enabled in the Advanced Settings for the project.