Hi Zia,
From the message you sent here it seems like that you are calling a page in the microflow which expects an object RestServiceHelper and you are passing a different type of object to that page. You should Create a new RestServiceHelper and pass it to the page or Pass the correct RestServiceHelper object to the page if it is accessible in the mciroflow .
Is this page Called from a Navigation and from there you are calling a microflow to call the rest service ?