Google Analytics conversions reported via Measurement protocol are missing device and browser data

Question

We currently use gtag.js on the frontend and report conversions through the API Measurement Protocol. This setup works well for us in terms of conversion attribution, as conversions are correctly attributed.

However, we’ve noticed that the conversion events lack important data, specifically the "device" and "browser" information.

According to the documentation (https://developers.google.com/analytics/devguides/collection/protocol/ga4/reference/events#purchase), it’s not possible to manually add this data to the purchase event. The only way for conversions to be associated with the correct session—and thereby inherit details like the device and browser—is by ensuring they share the same session ID. While this method works for attribution (i.e., medium and source are correctly applied), other session data such as device and browser is not being captured.

To illustrate the issue:

• In screenshot1.jpg, you can see the conversions correctly showing the medium and source.
• In screenshot2.jpg, however, the same conversions have "(not set)" in the browser and device columns.

Do you experience the same issue where conversions reported via the GA4 Measurement Protocol are missing browser and device data? The conversions are paired with the user's first visit event, so these missing values should be filled, but they are not.

*Edit This question is different from this StackOverflow post. The mentioned question is about sending the User-Agent to the Measurement Protocol, while my question is about conversions missing browser and device data. I am not attempting to send this data with the conversion, as that is not possible. Instead, conversions reported via the Measurement Protocol should automatically be paired with the user's first visit event, which should populate these fields, but this is not happening.