If you see this message when attempting to delete a pipeline, it means that the pipeline cannot be deleted because it has projects connected to it. This applies regardless of the project's state (e.g., open, won, or any other status).
To delete a pipeline with connected projects, follow these steps:
Navigate to Projects - List in the left menu
Use the filters to filter on the specific pipeline that you want to remove
Click on the three dots to the far right next to the project
Choose to "remove" or "edit" the project. If you choose to edit you can easily move the project to another pipeline. Scroll down to "pipeline" and choose another pipeline.
When you have moved all the connected projects you navigate back to;
Administration - process and the tab pipeline to delete the pipeline.
Congratulations! You have successfully deleted a pipeline with connected projects.