In order for us to work on your integration, you'll have to enable custom app development for your Shopify store. We'll talk about what that means, and how you should go about it, in this article.
Enabling Custom App Development
To begin with, only the store owner can enable custom app development, so make sure that's the account you're using to log in to the backend of your Shopify store. Once you're logged in, go to the Apps menu, and click Develop Apps. From there, you should be able to click on Allow custom app development. Doing so will present you with a terms screen, and you'll have to click Allow custom app development
You can read more about this on Shopify's page about this process here. If you have any further questions, please feel free to get in touch with your project manager for additional assistance using the Messages function in the onboarding center.