The couponRejectionReason-object will contain a string which can have the following text:
will be returned if the transferred coupon is wrong
will be returned if the campaign the coupon belongs to, is currently not active
will be returned if the coupon redemption limits have been reached
will be returned if the given coupon value does not match the recipient
will be returned if none of the reasons above fit the rejection. Usually, this implies that the coupon is valid and in an active campaign, but there were other conditions in the campaign rules that were not met.