Node.js API Shipment Integration

The Project is about creating a Node.js ([login to view URL]) for a Shipping Integration between a Cloud Platform and a Courier Service . Actually there are a demo glitch project to see and test how it works from this Cloud Platform, what I need is to make the same [login to view URL] for a real Courier that we need to link. I have the API documentation from both, the [login to view URL] is used to mach this 2 diferent systems, but basically from the Cloud Platform a JSON it´s send (Request) and from the Courier a (Response) is returned. All the fields are correctly descripted, basically when the Cloud Platform sends a JSON with shipment data (Name,Address, Country, etc..) the Courier Service returns a Response that it´s the validation of the info and a label coded as a ZPL or PDF corresponding to the delivery shipment label. Basically all the couriers works at this way, we have both API Keys, from Cloud Platform and Courier, in next weeks we will like to add more couriers that practically will be the same changin specific info from other couriers. Finally I would like to have a Postman Environtment to test directly the Courier Service and "POST" outside from the Cloud Platform to check possible errors and future new delivery methods. We have limited budget because it´s an integration where both sides are documented perfectly and it´s the normal way that e-commerce works with Courier companies, I will publish the API from those that can reach this project asap.