Upload a deck, upload the images it refers to, and check what is already here.
Set on the server as SLIDEMGR_UPLOAD_TOKEN. Kept in this tab only, and sent as a header so it never reaches the web-server log.
SLIDEMGR_UPLOAD_TOKEN
Letters, digits, . _ -. This becomes the deck id in ?deck=…, so keep it short and stable. Uploading over an existing deck keeps the old copy in _replaced/.
.
_
-
?deck=…
_replaced/
Stored in the deck assets folder and served at assets/<name>. Keep the filename you refer to in the deck — it is the name, not the path, that has to match.
assets/<name>
Tap Copy tag and paste it straight into a slide's text.