API creation between EPOS system and order management system.

I have 2 pieces of software that both have open API's that id like to link together.
We use a company called storefeeeder for our order management system and Vend for our EPOS system.
We need to get basic communication between the two.
Products / prices and inventory on storefeeder need to be synced to vend then a sale on vend needs to go back into storefeeder aswell as deducting the stock level on that order.

Here are the links to the companies API documentations hope this helps.
Storefeeder: rest.storefeeder.com
Vend: https://docs.vendhq.com/docs/client-api-reference

I hope this is enough info for you to have an idea on what im looking to do?
Any questions please let me know.