It's very important that you create customers, memberships, and coupons in Memberstack first. Memberstack can only recognize objects in Stripe if they were first created in Memberstack.
What to do if you created a customer in Stripe.
What to do if you created a membership plan in Stripe.
We recommend deleting the membership plan and recreating it in Memberstack. There's a very good chance assigning a customer to a plan you created in Stripe will cause the system to error out.
What to do if you created a coupon in Stripe.
It's okay to keep the coupon & manually apply it to customers accounts in Stripe, but you can't share the coupon code. If a new member tries to redeem the coupon during checkout, everything will error out.