How can we make double spend transactions? Can anyone explain? We have spent all btc in the devolpment, we have only 0.0004btc
Depends on your wallet...
For example, if you use electrum, you can enable coin controll, pick one (or multiple) unspent outputs from the coins-tab, right click, spend, enter a receiving address and a very low fee (you need to enable manual fee selection to).
When you created your transaction, click on the "preview" button instead of the send button, then sign the transaction and save it (do not broadcast). Close the window
In the next step, select exactly the same unspent outputs, spend, enter a different receiving address, enter a much higher fee, preview, sign, save.
You now have 2 unbroadcasted, signed transactions that spend the same unspent outputs.
Theoretically, the one with the lower fee/byte ratio has less chance of getting confirmed. However, there is no guarantee. The second transaction (with the higher fee/byte ratio) will usually not broadcast so good as the first one (since the first transaction will already be in the mempool of many nodes).
If you use core, you can create a double spending tx from the cli or from the debug window... You'll need to use following commands:
- listunspent
- createrawtransaction
- signrawtransaction
It's all pretty basic stuff... You should learn these basics before attempting to build a paywall. Also, there is hardly ever a reason not to develop on the testnet. I've had a client lately that insisted on testing on the main net to, we've lost a lot of money due to high transaction fees without any reason
