Treatment of Coupons in lieu of Joining Fees

If I am an E-Commerce operator and pay commission to the website owners who refer people to my website. I charge them (let's assume) Rs. 1000 as joining fees for affiliate marketing and provide them a coupon of Rs. 1000 in lieu of it which they can use to buy products on my E-Commerce platform?

Can somebody please guide me the GST implications on both the parties?

What if I charge the affiliate Rs. 1000+GST @ 18% and give him a coupon of Rs. 1000?