You need your Project Token to track events to Mixpanel. Mixpanel uses Project Token to ensure that events that you send are routed to your project.
You can find it in the Project Settings (opens in a new tab) page under "Access Keys"
The API Secret is used to backfill historical events into your project via our Import API and to export data out of your project via our Export APIs.
You should not share your API Secret, since it can be used to export data from your Mixpanel project.
You can find it in the Project Settings (opens in a new tab) page under "Access Keys", right below Project Token.
Service Accounts (opens in a new tab) are a more advanced form of authentication that is used to grant temporary access to a subset of Mixpanel projects within your organization for certain APIs.
Service Accounts are not necessary to send data to Mixpanel or export data out of Mixpanel.