eth_sendTransaction

Not supported by Infura

The eth_sendTransaction JSON-RPC method is not supported because Infura doesn't store the user's private key required to sign the transaction. Use eth_sendRawTransaction instead.

You can use web3.eth.sendTransaction, which in turn signs the transaction locally using the private key of the account, and sends the transaction via web3.eth.sendSignedTransaction, which is a wrapper for eth_sendRawTransaction.