While some protocols require value attached to OP_RETURN outputs, this otherwise seems like a mistake.

Setting the value to 0 should really be done by the wallet/script creating the transaction (like createrawtransaction does for `data` outputs). However, as an additional check, similar to the high-fee check, sendrawtransaction could also check for non-zero value OP_RETURN outputs.

This should be configurable by a new RPC argument.

See also https://transactionfee.info/charts/output-opreturn-amount/

#### Useful skills:

* Bitcoin Core RPC code
* Transaction output types
* Bitcoin Core functional tests

#### Want to work on this issue?

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{
public:
    std::string methodName; 
    int paramIdx;           
    std::string paramName;  
};
/**
 * Specify a (method, idx, name) here if the argument is a non-string RPC
 * argument and needs to be converted from JSON.
 *
 * @note Parameter indexes start from 0.
 */
static const CRPCConvertParam vRPCConvertParams[] =
{
    { "setmocktime", 0, "timestamp" },
    { "mockscheduler", 0, "delta_time" },
    { "utxoupdatepsbt", 1, "descriptors" },
    { "generatetoaddress", 0, "nblocks" },
    { "generatetoaddress", 2, "maxtries" },
    { "generatetodescriptor", 0, "num_blocks" },
    { "generatetodescriptor", 2, "maxtries" },
    { "generateblock", 1, "transactions" },
    { "getnetworkhashps", 0, "nblocks" },
    { "getnetworkhashps", 1, "height" },
    { "sendtoaddress", 1, "amount" },