Can I see a secret again?
No. A secret appears once when the key is created. If you lose it, revoke that key and create another. The masked value and key_ identifier cannot authenticate a request.
When do I need a live key?
A test key reads the sandbox fixture. A live key reads the published live catalog and requires an eligible paid plan. Changing a test key's prefix does not turn it into a live key.
How do I rotate a key?
Create a replacement, deploy it to your server, verify a request, and revoke the old key. You need a spare active-key slot for an overlap. Never revoke the serving key before the replacement is ready unless you intend an interruption.
Why can I not create another key?
The account may have reached its plan's active-key allowance or be inactive. After a downgrade, existing keys are retained, but new creation stays blocked until there is room under the new limit.