2. use private china (private network). If you reconnect failed or miss connect,
3. private network best good action is
Sometime you sure private network is work and ok. But check netowrks list failed, this time just redo Custome Network then everything is ok.
4. How to know private network have web3 and ok?
Just broswer web EX：http://192.168.9.10:38545 get 200 ok, sure web3 is ok.
5. geth rpc be careful
Fire time Open everything：--rpcapi "db,admin,debug,miner,personal,txpool,eth,net,web3" --rpc --rpcaddr "0.0.0.0" --rpccorsdomain "*" --rpcvhosts=*
check ok then remove or fix setting. EX：fix 0.0.0.0 => 140.140.140.140 then check again. If can't connect, you know which parms have problems.
6. smart contract
https://remix.ethereum.org/
https://solidity.readthedocs.io/en/v0.5.2/introduction-to-smart-contracts.html#simple-smart-contract
This example is simple for test.
use injected Web3 that call metamask. I try use Web3 Provide always failed. Don't wast time.
Error: invalid sender get this error. metamask custome network have one option
Try to put, sure connect, Then remove........ problem is this.
Why try put and remove. Because I try to put smart contract, get this message, then put chain id. Still get error message. Then I test for remove again, test private is ok or not. This time is success..........
PS：reload remix ethereum website maybe can fix bug
7. Why are MetaMask transactions taking a long time? MetaMask 交易為何十分耗時？
To ensure transactions are received in the correct order, each Ethereum transaction comes with an incrementing nonce. If you've used an account in MetaMask on a different network, you'll need to reset the nonce value. Click on the settings icon (3-bars), Settings, Reset Account. The transaction history will be cleared and now you can resubmit the transaction.
為了確保能夠以正確的順序接收交易，每個以太坊交易都會隨附累加的 nonce。 如果您將 MetaMask 中的帳戶用於不同的網路上，則必須重設 nonce 值。 請依序按一下設定圖示 (3 橫列) [設定]、[重設帳戶]。 交易歷程記錄將會清除，屆時您即可重新提交交易。
https://docs.microsoft.com/zh-tw/azure/blockchain/templates/ethereum-poa-deployment#why-are-metamask-transactions-taking-a-long-time
8. Do I need to specify gas fee in MetaMask? 我是否需要在 MetaMask 中指定燃料費？
Ether doesn't serve a purpose in proof-of-authority consortium. Hence there is no need to specify gas fee when submitting transactions in MetaMask.
乙太幣在權威證明聯盟中派不上用場。 因此，在於 MetaMask 中提交交易時，無須指定燃料費。
https://docs.microsoft.com/zh-tw/azure/blockchain/templates/ethereum-poa-deployment#why-are-metamask-transactions-taking-a-long-time