Test mode versus live
A Stripe key is either a test key or a live key, never both. SSA shows you which one is connected and lets you switch, but switching is a deliberate action, not a toggle.
What a test key shows
A key starting with sk_test_ or rk_test_ puts SSA in Test mode. Everything SSA shows, your subscriptions, customers and payments, comes from Stripe's sandbox, not your real business. The Environment control on Settings > Payment Providers has a hint that says it plainly: "Use Test to verify with sandbox data before going live."
A key starting with sk_live_ or rk_live_ puts SSA in Live mode, and the numbers you see are your real data.
How to switch between Test and Live
While a key is connected, the Test / Live segmented control is locked: you cannot change it without disconnecting first.
On Settings > Payment Providers, click Disconnect (see Rotate or disconnect a key for the confirmation step).
The Test / Live control unlocks. Choose the environment you want.
Paste a key whose prefix matches that environment, then click Connect.
What happens to your data when you switch
Disconnecting does not delete anything SSA has already synced: customers, subscriptions, payments and invoices from the previous key all stay in your reports. Connecting the new key does not delete them either, and it does not start a new sync by itself.