tpTrackingplan answers
Whether you have the classic client-side GTM setup or you are already fully advanced with GTM server-side tagging, you can use Trackingplan to check if the migration works.
Trackingplan automatically discovers the tag implementation you have in your Universal Analytics data layer. That way, you can quickly check if your events are being fired according to your specifications every time you migrate any of your tags to GA4 to can ensure you never lose data throughout the process.
If you’re feeling worried about migrating and the implementation process or you are unsure of where to start or what to do next, Trackingplan's GA4 migration checklist has the solution to help you transition successfully and smoothly.