Google Tag Manager / GA4 missing a lot of data

[cricom]

I am going to try to make a long story short(er).

I do marketing consulting for web hosting companies. The owner of one company had some concerns whether the analytics transitioned to GA4 correctly. I transitioned GA4 to Google Tag Manager code and the code is correctly inserted  in the website's and WHMCS headers. The "purchase" conversion tag is in place and capturing things (at least I see this data).

For my first test order I used a UTM link that I placed on an outside website. Made an order (new domain registration) while watching the live code to see if the tag is present. It is. The next day — nothing. I see users from a test website arrived, events took place, but the purchase wasn't captured. Beyond my own order,  on that day GA4 captured 36 purchases on 58 actual orders. For the week, GA4 shows only 182 orders instead of actual 295. That's 38% less captures than reality.

I've switched GA4 to "device only" identity reporting. I verified no ad blocker is in use and I am not blocking statistical cookies either. GA4 still reporting lower numbers.

We then install this module:
https://github.com/websavers/WHMCS-Google-Tag-Manager

For my second test, we use debug mode. Using the same UTM link, we monitor activity. I see myself arriving, I see myself scrolling and looking at pages. I even see add_to_cart and begin_checkout. Order domain and web hosting package this time. Then, nothing again. If anything, yesterday along GA4 missed 58% of captures.

I feel there is a 'deficiency' in how WHMCS pushing data to Data Layer. My next step would be to create a custom HTML hook, but I am hopeful someone genius here can give me a better idea what to do.

Another thing I noticed is that GA4 shows more activity related to hosting plans, but not domains. What I mean is the only time it captured begin_checkout tag was only when a hosting plan was added to a cart. 

Missing so much data is borderline ridiculous and makes marketing decisions very difficult.

[bellafronte]

I recommend this module available on WHMCS Marketplace https://marketplace.whmcs.com/product/3118-google-tag-manager-enhanced-data-for-whmcs

Google Tag Manager for WHMCS by Mimir Tech has a lot of properties on Data Layer and is built to cover all aspects needed by the Google Marketing Platform as full Google Tag Manager integration, (correct) purchase tracking, and enhanced user-provided data.

Besides, this module follows other standards that permit to you use the provided data in other tags and marketing platforms like Meta Ads (Facebook Ads, Instagram Ads, etc), TikTok ads, and other tags.

Full specification features are provided on website https://www.mimirtech.co/whmcs-google-tag-manager/