Coupon not applying when using paypal

When a user uses a coupon code at the registration page, registers on the next page, then click the paypal buy now button, they are redirected to paypal (as they should be) but the coupon code does not apply to the total.

Is there a correct workflow to using coupon codes?
The coupon code is in the coupons section of the membership plugin with a discount of 100% and it is in the valid date range.

Please help!