Create the discount in Shopify as a discount code (not an automatic discount) and copy the number at the end of its web address: that's the discount ID.

Plans & Perks > Membership Perks next to your plan > Create New Membership Perk (Add New Membership Perk once the plan has perks) > Member Discount. Each plan has its own perks: Clone to Other Plans copies one to the plans you choose.

Appstle applies one discount code per order, and a plan can have only one Percentage or Fixed Amount perk. If you change a discount in Shopify, enter its ID in the perk again.

Percentage, Fixed Amount, Buy X Get Y and Free Shipping use the discount ID and a Member Benefit Message. With Auto-apply discount at checkout on, the code goes into signed-in members' carts and the message shows as a banner on your store. The Point Of Sale types take a percentage or an amount instead of an ID, and your staff apply them to a member's sale in Shopify POS.

Email Discount Code To Members and Gift Card To Members send each member a reward on a recurring schedule, after every successful payment, or once, on the first membership purchase. Codes go out in the Recurring Discount Code email (More > Email Settings), and Shopify emails the gift card.