If you have ‘Activate “Create” capability for posts/pages/custom post types’ option active at ‘Settings->User Role Editor’, role should have capability ‘create_shop_coupons’ to see missing “Add Coupon” button.
I confirm the bug – User Role Editor did not added such capability automatically. I will prepare the fix.
Quick turnaround – add ‘create_shop_coupons’ capability manually.
