Thanks for this information, I have used fixedfloat and I am okay with their service but I was not aware that OKX offers such service, please can you give me a guide on how to navigate OKX website to get to the point of instant swap?
There's no instant swap with OKX. It's a CEX, like Binance. So you need to:
Deposit your funds to the exchange's wallet -> wait for confirmations -> go to the trading page and create the order -> withdraw.
If you're interested in other instant exchanges, you can check this list (not all of them support LN though):
https://bitcointalk.org/index.php?topic=5218464.0-snip-
AFAIK, Thorswap doesn't support the lightning network. I'll also have to disagree about the costs. Since they have low liquidity, you usually find yourself dealing with very bad rates.