From Alpaca's live dashboard (not paper): API key ID and secret. They are tested with Alpaca before saving and never shown again. Saving new keys switches live trading off.
Trading switch
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Security question
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Asked with the page password to pause or resume, to switch live trading, and to save live keys.
Machine
Alerts
Only problems are sent. Saved keys are never shown again; leave a box empty to keep what is saved.