Who can help if discounted codes fail to apply to abandoned carts?

I've been running my Shopify store for two years now, and discount code issues are driving me absolutely crazy. Just last week, I noticed several customers abandoning their carts after our promotional campaign because the codes weren't applying correctly. We're not talking about a small problem—this is potentially thousands of dollars in lost revenue. I've tried manually troubleshooting, checking Shopify settings, and even reaching out to our app developers, but nothing seems consistent. Some codes work perfectly, while others just... disappear. The frustration is real. Our marketing team crafts these amazing campaigns, we drive traffic through expensive Meta ads, and then at the final moment, a technical glitch destroys our conversion potential. It feels like we're losing money right at the finish line, and every abandoned cart represents not just lost immediate revenue, but potentially a long-term customer relationship. I need a solution that can automatically manage these discount codes, ensure they're applied correctly, and give me peace of mind that our promotional strategies won't fall apart due to technical limitations.