Let the user pay a fee to use a function

Smart Contracts
1

Hi!
I don’t understand how to use “payable” functions.
How can I ask that the value sent is equals to an amount I choose?
How can the user know how much to send to this function?
Thank you.

2

Hi,

There are several ways to do it depending on your dapp design or how you choose to interact with the contract, one way could be this:

contract A {
 uint fee;
 constructor(uint _fee) public {
  fee = _fee;
 }
 function payableFunctionName() payable external {
  require(msg.value >= fee);
  //...Logic
 }
}

How the user would know how much it needs to tranfers you could expose a function to get the fee, or if you are using a dapp tell the user over there reading the fee variable of the contract:

function howMuch() external returns(uint) {
 return fee;
}
1 Like
3

Thank you really much!

4