Why is the currency switcher not showing on my storefront?

Go to Store Settings → Multiple Currencies and check:

1. Enable multi-currency (show the currency switcher on the storefront) is ticked.
2. At least two currencies show ACTIVE in the list. A currency marked HIDDEN is not offered, so click Activate on it. With fewer than two active currencies the switcher stays hidden.
3. No currency is stuck at a Rate of 1. The page warns you when one is, and that currency will not convert. Click Refresh rates now to fix it.

The switcher appears in the store header. When a shopper picks a currency, the page reloads with all prices in that currency.