For koinvote, you don't need to open a Lightning Channel. The Lightning Network (LN) is useful for instant and inexpensive payments, but it's not designed for Bitcoin message signing.
Why LN isn't suitable here
LN channels are used for exchanging off-chain payments, not for proving address ownership.
Message signing requires an on-chain private key associated with your BTC address.
LN wallets like Muun or Phoenix don't allow you to sign a message in the same way as Electrum or Bitcoin Core.
Practical solution
Deposit a few satoshis on-chain into your regular Electrum wallet.
Use the Sign Message function in Electrum.
Copy the signature and paste it into koinvote.
Reliable alternatives
Bitcoin Core with the signmessage command.
Ledger or Trezor offer a built-in signature function.
Trust Wallet (depending on the blockchain).
Conclusion
You don't need to open an LN channel for this operation. The simplest and most secure way is to remain on-chain with Electrum or another compatible wallet.