I think the first thing is make sure your endpoint_pipeline is set up correctly.
You can try to return all active pipeline to see if the pipeline you want to call is in the list:
endpoint_list = PipelineEndpoint.list(workspace=ws, active_only=True)
endpoint_list
I also attach the guidance of how to deploy a pipeline here for your reference:
https://github.com/Azure/MachineLearningNotebooks/blob/master/how-to-use-azureml/machine-learning-pipelines/intro-to-pipelines/aml-pipelines-setup-versioned-pipeline-endpoints.ipynb
Regards,
Yutong