error practice formatting question

[Hamobcdev]

 function fund() public {
        // want to be able to set the minimum fund amount in usd
        // 1. how do we send ETH to this contract
       
       require(msg.value.getConversionRate() >= MINIMUM_USD, "Didn't send enough!");
        funders.push(msg.sender);
        addressToAmountFunded[msg.sender] += msg.value;
    }

TypeError: "msg.value" and "callvalue()" can only be used in payable public functions. Make the function "payable" or use an internal function.

What is my error here please?

[Hamobcdev]

This is such cool course, thanks Free code camp and Patrick