Please read and learn more about how LN works.
  1. bitcoin onchain are the same sats on LN.
  2. On LN the sats are actually delayed txs that are not yet broadcast.
So there's no such thing as "convert" sats from onchain to LN. What you wanna say is a submarine swap from onchain into a LN channel. Resources:
Thank you. I learnt something in your comment.
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