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Can someone please explain how parameters for the smart contract are encoded when making a JSON RPC call with the eth_sendTransaction method? For example, I have a mint function in a smart contract that needs user address and amount unit256 as 2 parameters. So how to encode them and pass them to the data field?

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Usually they are automatically by a framework like web3.py using ABI encoding based on ABI files. You don't need to use eth_sendTransaction JSON-RPC method directly.

You can find some examples here how Contract proxy objects are created an d how you can work with them.

The web3.py ABI + contract proxy object model applies to any programming language.

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I have a mint function in a smart contract that needs user address and amount unit256 as 2 parameters. So how to encode them and pass them to the data field?

You should declare the user address as a Solidity address type, the int amount can be a simple int. Both JS and Python Web3 implementation will provide you a function to create proper address type that can be used by the contract function.

The Python example of the correct address variable implementation:

from web3 import Web3
userAddress = web3.toChecksumAddress(raw_address)
amount = 10000000000000 // amount in wei
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  • So how to combine and encode these results and concatenate them with encoded function (mint) to complete the data field? I'm reading this doc but don't understand how to combine them into the data field. ethereum.org/en/developers/docs/apis/json-rpc
    – user101488
    May 31 at 1:17

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