You are creating a plug-in for an app that helps government employees get a proof of vaccination card. You must add the following information to a vaccination record before a proof of vaccination…

PreValidation is the earliest stage, primarily for validating data or cancelling operations, not for modifying the entity's data prior to creation.

PostOperation occurs after the main database transaction has completed, making it too late to modify data before the record's initial creation.

MainOperation is the core platform operation itself (e.g., actual database write), where custom plug-in code cannot directly execute as a separate step in the event pipeline.

The PreOperation stage allows custom logic to modify data before the main platform operation (like record creation) executes, but after initial validation. Registering the plug-in at this stage ensures that the vaccination type, date, and administrator's name are added to the record before it is officially committed to Dataverse.