Google Analytics 4 (GA4) handles sessions differently from Universal Analytics. In GA4, there is no explicit way to manually end a session since it is based on an automatic algorithm. A new session is started after 30 minutes of inactivity, or at midnight local time and there is no built-in way to manually reset this.

You might want to consider other workarounds to get the insights you need:

1. User Pseudonymization: One possible solution could be to assign a unique pseudonym or ID to each user and send it as a user_id parameter with each event.

2. Event Customization: If you need detailed tracking for each transaction, you could create and track custom events for each step of the process. This would give you visibility into each user’s journey, regardless of whether it is technically considered as one session or multiple.

3. Cohort Analysis: GA4 has the ability to group users together with shared characteristics (e.g. transaction completed) with its Cohort analysis feature. This might provide the insights you need.

Be sure to comply with Google Analytics’ Terms of Service and any relevant data privacy laws and regulations if considering pseudonymization.