insufficient funds for gas * price + value in OnChain wallet

My father-in-law trying to transfer ~150 ETH from an OnChain wallet into a Crypto.com exchange wallet, and every time we attempt it we get the error "insufficient funds for gas * price + value". We tried sending only 140 so there should be more than enough left for gas, and even tried only sending 50, but each time got the same error. From my research it seems like maybe we need to increase the gas limit, but it's not really clear to me what it needs to be set to. We tried setting it to 100,000 and 10,000,000, and no matter what we do it says the same error.

Additional info: My father-in-law put all this money in ETH so he could give it to scammers and we're trying to get it back before he gives it to them. It's possible that somehow we're in a situation where it's irretrievable, but as far as I can tell the this is a legitimate OnChain wallet that he has real ETH in, so I'm not sure why it wouldn't let us send to an exchange wallet.