What Sovryn does is to exchange their own BTC and RBTC to do peg ins and peg outs with a fee.
A real peg in requires one to send BTC to a RSK address where they’re locked during many BTC blocks before you can get the RBTC. A similar process is required to peg out RBTC, which is now back.
Sovryn does not use this misguided terminology for fast BTC service, they prefer swaps instead. FastBTC Relay | SOVRYN