Postmates integration with Shopify Shipping/Carrie

so we are looking to integrate this application:

https://postmates.com/developer/docs into our Shopify platform.

For how it works please check: http://blog.postmates.com/post/104856343907/a-technical-perspective-on-the-postmates-api .

So we are looking for add a Carrier Service to our store. And As Postmates provides services to few regions as follows we will add other mutiple shipping options for non-Postmates supported regions.

Postmates is currently available in the San Francisco Bay Area (San Francisco, East Bay, South Bay), New York City, Chicago, Los Angeles, Washington DC, Seattle, Austin, Boston, Philadelphia, Miami, San Diego, Denver, Las Vegas and Orange County.

I have contacted both Shopify and Postmates, who both say there is no app already built to directly integrate this into their account. With that said, Postmates claims that it has been done before where a user creates a Private App and connect it through API key that way. Could you please advice on below: 1) Review the documentation that I sent over in the above link 2) Research how to integrate this into a Shopify backend, any way possible?...whether through private app or not, but through API for sure. 3) potential solutions for postmate shopify API integration 4) potential solutions for app creation and/or any management of the process.

Also please note: So basically we want to add Postmates shipping service for some regions only ( as it supports few regions only https://postmates.com/help Topic : "What cities is Postmates available in?" ) and for other regions we will have different shipping charges+ methods etc...

So at backend which things & how we need to setup the things.As per this : http://docs.shopify.com/api/carrierservice

Is there any limitations or restrictions??

Please advice if I am missing any information or any specific detail to mention here.

Is there any creative folks who like to dive deep into space??

The Shopify API's carrier service resource (http://docs.shopify.com/api/carrierservice) is indeed the solution you're looking for.

Whenever a customer of your Shopify store is placing an order during checkout, after he has entered his billing & shipping address, Shopify can send a rate request to the carrier service you have registered. This post request contains all data about the items in cart and the customer.

Your carrier service app needs to accept this POST request, calculate the corresponding shipping rates - in your case by yet another API call to the Postmates API - and then return a JSON response in the format that Shopify defines in the docs. If all goes well, the shipping rate(s) your app has returned will then be shown in the checkout.

You can code your app such that for the cities that Postmates doesn't support, your carrier service will return no rates.

We've built such an integration with Shippo (https://apps.shopify.com/shippo), supporting many other carriers. Let me know if you need further help.