Shopify SaaS Integration Help

[GLBdeveloper]

Hi,

We have an inventory management SaaS which we would like to integrate with Shopify so that our SaaS users can sync their inventory with their Shopify store inventory.  Or vice-versa, sync their Shopify inventory into our inventory management SaaS.  Which Shopify API should we use?  Do we need to build a Shopify app?  Any guidance would be appreciated.  

This type of integration is very common with many SaaS out there.  This is one example of what we are basically trying to accomplish: https://www.stockandbuy.com/shopify-app-installation-guide/

[birdy247]

I am also interested in this, although we would also like to create an order when its made on our SaaS with shopify so that it can be fulfilled using another marketplace app.

Which API do we need.  Are there any docs on this?  I see lots of unanswered questions around this so wondering if there is a better means to ask this question?

Thanks