Keys are created per company on the API keys screen. There are two kinds, and the difference is where they are allowed to be.
pk_live_…is public. Write only, tracking scopes, restricted to the domains you name. It is safe in a browser because there is nothing it can read.sk_live_…is secret. Server side, full scopes, and it must never reach a browser or a repository.
Scopes
events.writerecords events, page views and conversions.leads.writecreates and updates leads.bookings.writecreates and updates bookings.links.writecreates tracking links.reports.readreads figures, campaigns and links.
How they are stored
Only a SHA-256 digest is kept, with the prefix in clear so a key can be recognised in a list. A key shown once is shown once: if it is lost, issue another and revoke the old one. Nobody here can read it back to you.
Send the key as Authorization: Bearer …. Requests are rate limited
per key, and a revoked key is refused immediately rather than at the end of its
period.