Problem in verifying the signature in smart contract which was signed by eth.personal.sign() in web3

// Web3 code

let amount = 55;
let messageToSign = `Please sign the message for claiming the reward amount of 
${amount} tokens!`;

let signature = await web3_obj.eth.personal.sign(messageToSign, account.toString());

// Smart contract code to verify the signed message to get the signer's address

    function getSigner(uint _amount, bytes memory _signature) 
    public 
    pure 
    returns(address) {
        bytes32 _prefixHash = 
         ECDSA.toEthSignedMessageHash(keccak256(abi.encodePacked("Please sign the 
         message for claiming the reward amount of ", _amount, " tokens!")));
        
        return ECDSA.recover(_prefixHash, _signature);
    }