This is an example call for rpc_modules.
{
"jsonrpc": "2.0",
"id": "1",
"method": "rpc_modules",
"params": null
}
{
"jsonrpc": "2.0",
"id": "1",
"error": {
"code": -32601,
"message": "The method rpc_modules does not exist/is not available"
}
}