You may be confused. Looks like you tried to do a Btc payment with onchain funds when you have only lightning bitcoin.. think of onchain bitcoin and lightning as two seperate layers, you can’t pay onchain addresses with lightning funds. Similarly, you can’t pay lightning invoices with onchain funds. You would need to settle the Lightning channel on chain by closing your open channel to make this onchain bitcoin. Not sure if mutiny has this capability, this is why many people run nodes so they can open and close Lightning channels and return Lightning bitcoin to your onchain wallet