To add Selling Plan Groups to your products, first you need to assign them to these individually and then create a product template in your Store Theme to add Sharpei's subscription button.
Add your Selling Plan Groups to your Products
Go to your products page and select a product which you'd like to add a group.
Inside the product, look for the Purchase Options section
3. Click on Add purchase option and hit on Select existing option.
Select Sharpei Connect
Choose the Selling Plan Group
Click on Complete Setup
Add Sharpei's subscription button in product templates
The easiest way is to duplicate one of your products template, then hide the button you're using and replace it with Sharpei's one.
STEPS:
In your Shopify account, go to Online Store > Themes Click > Customize
Search for Products in your home page
Select "+ Create template"
Give your new template a unique name - e.g subscription XXX product - and select which existing template you want to base it on.
In your new product template click on 'Add block' and search in apps for Sharpei's Subscription Product Form and select it.
🚨 Make sure to hide the other cart button so that it only appears Sharpei's widget.
6. Save
Assign the subscriptions template to your products
Go to the products you want to add the template in Products page, and assign it inside the Theme template section. Then use the drop-down menu to select the new template you just created.
To assign templates in bulk, take a look at Shopify's Helpcenter.