Katy here from Shopify. I hope all is great with you, and welcome to our Community here.
When building a Shopify app, you'll want to first set yourself up with a free partner account. You can do so here if you have not done so already. We have a great FAQ guide here which walks through the details of this program.
Once you have this set up, you can then begin creating an app using our open API. We have some great guides and resources to help you out with this. I have added some links below for you to check out:
Based on the functionality that you are looking for, there are certain existing apps in our app store which may achieve this without you having to create your own app/ app for your client. I have included a link to these here, just in case this was a route you may like to consider.
If you do however decide to build your own app, we have our developer board here in case you need some extra help along the way.
I hope this helps you out!
Hope you are doing good !!!
It's great to know you are bringing in Multi-Channel Selling into the picture as you sell on eBay, Etsy & Shopify. To have a better conversion rate it is very important to make use of reliable Integration Apps to link you're a Marketplace with Shopify.
Isn’t? Etsy Marketplace Integration App is out there in the eCommerce space to help you easily list your Shopify product on Etsy.
The app also helps you to edit and manage the Inventory, Price, Order etc. of your products.
One of the best parts of Etsy Integration Marketplace App is it based on Polaris theme which provides you similar Shopify user experience.
The App has a profiling feature as well which ensures the grouping of the Shopify products on the basis of Product Type, Vendor, etc. This helps to list & update products on Etsy effortlessly.
Hope this answer suffices your query. Have a great time selling on Etsy.