Economically the investor has bought a bond and sold a put option on the underlying, with the put premium funding the elevated coupon. A note paying 12% on a volatile single stock is charging that stock's implied-volatility, not offering free income.
At maturity, if the stock is above the strike or never breached the barrier, cash is returned with the coupon. Otherwise the investor receives shares worth less than the amount invested, keeping the coupon as partial compensation.
The asymmetry is the point to understand: upside is capped at the coupon regardless of how far the stock rises, while downside below the barrier is close to the full equity loss. See cash-secured-put for the equivalent position built directly.
Related: cash-secured-put, autocallable-note, structured-product, implied-volatility, put-option, issuer-credit-risk