You can add free gifts in specific subscription to make customer keep on ordering, and not to end subscription.
Step 1：SHOPLINE Admin > Products & Categories > Free Gifts
Click “+Add” to add a free gift.
For further information, please refer to Sales & Promotions: Free Gifts Promotion Settings.
Step 2：SHOPLINE Admin > Order Management > Product Subscription Management
Click “Setting Subscription Gift”
Step 3：SHOPLINE Admin > Order Management > Product Subscription Management > Setting Subscription Gift
2.Enter “amount” and “specific subscription”, then click “Select”
3.Select a gift, then click “Save”
4.Click “Update” to save your changes
After you complete setting, customer will get free gift in specific subscription.