Deployment from Modeler To Cockpit

I need to deploy from Camunda Modeler to Camunda Cockpit, but I need to implement a security gateway between those. How can I send a request from Camunda Modeler to my security gateway?
If I try to send something from Modeler to my microservice, then I have an error:

Parameter specified as non-null is null: method *.securitygateway.api.web.Controller.uploadDmn, parameter data

So looks like my Controller:

fun uploadDmn(@RequestBody() data: MultipartFile){


How can I resolve requests, if I use Spring Boot REST Api with Spring MVC?