We started sending purcahse event through the measurement protocol to our GA4 property and we disabled the GA4 native purchase event code on the thankyou page.

I have GA4 running on my site, and in my backend I store the user’s client_id and session_id. With measurement protocol on our backend, I send a custom trial started event when a user starts their trial, and I send a custom subscription paid event when a user pays for a full month. Both of these events use the same function in my code, so I know nothing is shifting between them: