Due to tracking restrictions and of stable work of the client-side tracking, your affiliates can lose up to 40% in the commission. It can be fixed by setting up server-side affiliate conversion tracking.
Stape created an Affiliate conversion tag for the server Google Tag Manager to track pageviews and conversions from affiliate partners. By setting up an affiliate pageview event, you take the URL parameter (in most cases, it's either affiliate ID or click ID) and store it in the browsers' cookie. You can set the lifetime of this cookie.
When conversion event triggers, you can fire the affiliate conversion event that sends requests with the configured URL and required parameters.
1. How to use affiliate conversion tag.
2. Affiliate conversion tag template.