Julie here from Shopify Support.
I can definitely see how important it would be to have discount codes still work with the Infinite Product Options app. Have you had a chance to review the help documentation over in the Hulk Apps Help Center? I took a look there and managed to find a help doc on how to use discount codes with their app; it looks like you'll just need to add some code to your cart.liquid theme file.
The help doc doesn't outline the code you'll need to add, so if you're still needing assistance, then I suggest reaching out to the Hulk developers directly. When it comes to third-party apps, the developers themselves are the best to assist since they know their apps inside and out. You can typically find the developers' contact information directly within the app itself, or under the Support section of their app page in the Shopify App Store. We also have some information on getting help with third-party apps that you should find insightful.
I hope this guides you in the right direction!