Shouldn't be too hard to fix. If you're passing additional data into the URL, it can be picked up in GTM easily. There are several potential solutions. I've debugged similar things before.
Relevant Skills and Experience
5+ years of Google Analytics, Google Tag Manager, AdWords, FB Ads, and general digital marketing experience with over 100 clients. Technically proficient with GTM/dataLayer/Google Analytics.
Proposed Milestones
€5 EUR - Assessment of problem (requires GTM/GA access).
€29 EUR - Propose, document and implement solution.
Additional Services Offered
€150 EUR - If you need more advanced Analytics configuration, I can provide it.
Is it a single-page application/website? Or an ecommerce platform (Shopify, Magento, Woocommerce)?