Simulation of run_operation of XTZ send gives Failed to parse the request body: No case matched:

Question

I'm dry-running an operation with an xtz amount that is close to my max balance to an unrevealed tz2 account on mainnet to get the fees.

When estimating for fees I run two RPC endpoints at the same time:

• /chains/main/blocks/head/helpers/scripts/run_operation with an empty 64 encoded byte array signature:

{
    "chain_id": "NetXdQprcVkpaWU",
    "operation": {
        "contents": [
            {
                "amount": "234023908",
                "storage_limit": "60000",
                "gas_limit": "800000",
                "kind": "transaction",
                "fee": "0",
                "destination": "tz2TrNfsT9zt1RW6oefQBrebLg8kMHbcvdRd",
                "source": "tz1...",
                "counter": "7613069"
            }
        ],
        "signature": "edsig...",
        "branch": "BLUJG76seoXDxuq8UBWDPvFPJv3StaVckxfijCtvemKmm3tzNYt"
    }
}

And

• /chains/main/blocks/<branch>/helpers/forge/operations with this json:

 {
    "contents": [
        {
            "amount": "234023908",
            "storage_limit": "60000",
            "gas_limit": "800000",
            "kind": "transaction",
            "fee": "0",
            "destination": "tz2TrNfsT9zt1RW6oefQBrebLg8kMHbcvdRd",
            "source": "tz1...",
            "counter": "7613069"
        }
    ],
    "branch": "BLUJG76seoXDxuq8UBWDPvFPJv3StaVckxfijCtvemKmm3tzNYt"
}

To get the bytes needed for the storage fee.

I'm in a situation where I cannot check the response of each individual call but I know the error I get is:

Failed to parse the request body: No case matched:
  At /kind, unexpected string instead of endorsement
  At /kind, unexpected string instead of seed_nonce_revelation
  At /kind, unexpected string instead of double_endorsement_evidence
  At /kind, unexpected string instead of double_baking_evidence
  At /kind, unexpected string instead of activate_account
  At /kind, unexpected string instead of proposals
  At /kind, unexpected string instead of ballot
  At /kind, unexpected string instead of reveal
  At /kind, unexpected string instead of transaction
  At /kind, unexpected string instead of origination
  At /kind, unexpected string instead of delegation

Usually the real reason can be found in between the list but, in this case, nothing else is returned. Is there any way I can investigate further about this error and its cause?

If the problem would be the amount I'm giving is too high, I'd be getting a cannot_pay_storage_fee kind of error, so I'm guessing the problem is elsewhere?