You need an access token to try the APIs. To get one, you need the refresh token from your Lightup API credential file.

Get a Lightup API credential

Login to the Lightup app.
At the bottom of the left pane, select the gear icon, then select API Credentials.
In the modal that opens, select Generate API credential.
In the confirmation message that appears, download your credential file.

Open the downloaded file using a text editor.
Copy the value of Refresh (near the end of the file). Be sure you only get the value itself— no quote marks or leading spaces.
Back on the API page, near the top right, make sure the URL points to the Lightup cluster where you generated API credentials. You'll need to change just this part of the URL:

Paste your refresh string into the BODY PARAMS refresh parameter (below), then in the right pane select Try It!.
In the response, copy the value of access - this is the access token you'll use with the rest of the APIs.
In a text editor, type Bearer, a space, and then paste in your access token. Copy the whole string to paste it into an Authorization parameter. Note that your access token does expire, but you can reuse the text file— just get a new refresh token, a new access token, and replace the old access token.

200