Problem when deploying a workflow + spring boot application on a remote server

I have a workflow and a spring boot application deployed on a remote server, I have implemented an API in the spring boot application to invoke the workflow. However I tried to execute the API via postman to invoke a workflow instance I get this error:
{
“timestamp”: 1547146873672,
“status”: 500,
“error”: “Internal Server Error”,
“exception”: “org.camunda.bpm.engine.exception.NullValueException”,
“message”: “no processes deployed with key ‘PatientAppointmentOperation’: processDefinition is null”,
“path”: “/camunda/startProcess/PatientAppointmentOperation/10”
}
PatientAppointmentOperation is the process id of my workflow.
Everythis is working fine when I deploy the spring boot application and the workflow locally, but not on the remote server.
Any help please?

You need to make a small change to your rest call.
You need to start the process by the key it looks like your starting it by the ID.

Can you show the full call your making and maybe also upload the model.

Thanks Niall for your reply.

The key definition is “PatientAppointmentOperation”, so I am using the correct key.
This is the API that I implemented in spring boot:

@ResponseStatus(value = HttpStatus.OK)
@RequestMapping(value = "/startProcess/{proId}/{businessKey}", method = RequestMethod.GET)
public ResponseEntity<Object> startSampleProcess(
		@PathVariable("proId") String proId, @PathVariable("businessKey") String businessKey) {
	RuntimeService runtimeService = processEngine.getRuntimeService();
	ProcessInstance processInstance = runtimeService.startProcessInstanceByKey(proId, businessKey);
	return new ResponseEntity<Object>("Process Started Successfully with process instance id : "+processInstance.getId(),HttpStatus.OK);
}

the full call I m making is a get request with this url : http://{address}:{port}/camunda/startProcess/PatientAppointmentOperation/10