Lesson 4: Remix Fund Me

[aviorn36]

Hi Community,
I have a fund me smart contract deployed to Goerali TestNet, the fund Me function expects at-least $50USD worth of ETHToken. And I do not have any Receive or Fallback function implemented. I wanted to test a scenario where I directly send the fund (value transaction) to smart contract using metamask without using fund me function which as per my understanding should allow but the transaction is failing and I am not very sure why it is failing. I have even set the Gas Limit bit high so that I know it is not because of insufficient gas.

Can you please help me figuring out if the block chain should allow such kind of transaction directly to smart contract and if yes what would be the issue here?

Please, do let me know if it is safe to provide link to failed transaction if that will help figuring out the issue with transaction?

[RoboCrypter]

@aviorn36 : Yes, you can provide your failed transactions No worry!

[aviorn36]

Really appreciate your help @abossofmyself . Below is the link of failed transaction. 'https://goerli.etherscan.io/tx/0x1c4d7fc3e29a833c66c0335df3ede25f8bd3a8791869a896958f578d8407c09b

[RoboCrypter]

@aviorn36 : I have gone through your failed transaction, As you stated you don't have a receive and fallback function!

That is the reason it is failing,

You should at least have one of the above functions, in your contract to receive funds directly to the contract.

• payable receive function or fallback function in order for your contract to receive funds directly :

  Just add this function : receive() external payable {} or fallback() external payable {}

It will solve your issue!

[othaime-en]

Hey @aviorn36 for your contract to receive/hold ETH, there has to be atleast one function marked payable In our case, it was the fund() function. However, in scenarios like the one you have where you want to send funds directly without using the fund function, we need to come up with a default function that sort of receives the funds. In you case, since you didn't set a fallback function, that's why you encountered an error because there is no way contract can sort of, hold/receive the funds you are sending to it. So if you don't want to use the fund function as the main way you send money into this contract, you have to set a payable fallback or receive function that will do just that. In your case, you could create a simple receive function as follows

    receive() external payable { }

This is enough. Or you could go an extra mile and add a fallback function. But this is just fine.
This implementation doesn't use the fund function so there isn't any limitation as to whatever value you can send (no minimum value) But if you still want to enforce the functionality of the fund function, you can just call the function inside the receive function as follows

    receive() external payable {
        fund();
    }

[aviorn36]

Hi @othaime-en , so in a way I can say that for a contract to have a default ability of holding token/ETH, I must implement one of fallback or receive special function that are payable.
So my transaction was failing as I did not explicitly triggered fundMe() function and since I just sent token/value only transaction to contract address it was not able to map to any defined payable function, hence the failure. Is this understanding correct?

[othaime-en]

@aviorn36 Yes. Exactly.
It is always good practice to have a fallback or receive function or both to account for all scenarios where someone sends funds to your contract.

[aviorn36]

@othaime-en once again Thank you very much :)

[alymurtazamemon]

@aviorn36 Exactly!