SOL is the native token of Solana - it's not an SPL token. To transfer SOL, use the solana command, not the spl-token command.

solana transfer --from <KEYPAIR> <RECIPIENT_ACCOUNT_ADDRESS> <AMOUNT> --fee-payer <KEYPAIR>

SOL is the native token of Solana - it's not an SPL token. To transfer SOL, use the solana command, not the spl-token command.

solana transfer --from <KEYPAIR> <RECIPIENT_ACCOUNT_ADDRESS> <AMOUNT> --fee-payer <KEYPAIR>

See the Solana Labs docs