Failed to fetch gas estimate when sending erc20

[ChuanqingYang]

    let value : String = amount
    let walletAddress = EthereumAddress(wallet.address)!
    let toAddress = EthereumAddress(to)!
    // contractAddress
    let erc20ContractAddress = EthereumAddress("0x94a91f7f24738b2b49d0d009aA0801a280D05eBb")!
    let web3 = self.getETHWeb3()
    let keyStoreManager = self.getETHKeyStoreManagerWithWallet(wallet: wallet)
    web3.addKeystoreManager(keyStoreManager)
    let contract = web3.contract(Web3.Utils.erc20ABI, at: erc20ContractAddress, abiVersion: 2)!
    let amountA = Web3.Utils.parseToBigUInt(value, units: .eth)!
    var options = TransactionOptions.defaultOptions
    options.from = walletAddress
    options.gasLimit = .automatic
    options.gasPrice = .automatic
    options.nonce = .manual(try! web3.eth.getTransactionCount(address: EthereumAddress(wallet.address)!))
    let method = "transfer"
    let tx = contract.write(method,
                             parameters: [toAddress, "\(amountA)"] as [AnyObject],
                             transactionOptions: options)!
    print(tx)
    let result = try! tx.send(password: password)
    complete(result)

Here is my error code & description: -32000 execution reverted
Failed to fetch gas estimate

[ChuanqingYang]

Finally i found what's wrong with my code

The amount what i'm set is ETH which is a wrong option.
let amountA = Web3.Utils.parseToBigUInt(value, units: .eth)!
ERC20 transation amount should be set what it's decimals be,use the below functions:
let amountA = Web3.Utils.parseToBigUInt(value, decimal: X)!
you should replace X with what contract requiered.