In ReCharge, you can create discount coupon codes for your customers to apply to their order. All discounts for subscription products must be created separately on ReCharge. This is as a result of a Shopify limitation. This also applies to universal discounts, such as 10% off all products. In that case, you will need to make sure that you duplicate that code in Shopify.

Below is the tutorial on how you will be able to achieve this.

https://support.rechargepayments.com/hc/en-us/articles/360008830533-Creating-Discounts

Please note: For discounts on subscription products only, discount codes must be created in ReCharge, not Shopify.  For discounts on all shop products (both subscription and one-time), you must create the same discount codes in both ReCharge & Shopify.