Standalone network error: tx_not_supported

Question

We have built a Standalone Network with 3 Stellar nodes as full-validators and horizon. Every node and horizon run the 18.0.4 version in a docker container and can access node's history thanks to nginx.

Here's one Stellar node configuration:

DATABASE="postgresql://dbname=core host=aws1_db user=stellar password=mynicepassword"
NETWORK_PASSPHRASE="Standalone Network ; February 2017"
NODE_SEED="SCZ2SZQUVMPECEDFMOXFAA4KG3A7IRNA62PIOX556XFUH7RMETRBHPQK"
NODE_HOME_DOMAIN="mydomain"

HTTP_PORT=11626
PUBLIC_HTTP_PORT=true
PEER_PORT=11625
NODE_IS_VALIDATOR=true
FAILURE_SAFETY=0
UNSAFE_QUORUM=true
RUN_STANDALONE=false
CATCHUP_COMPLETE=false
CATCHUP_RECENT=0

[[HOME_DOMAINS]]
HOME_DOMAIN="mydomain"
QUALITY="MEDIUM"


[[VALIDATORS]]
NAME="aws2"
HOME_DOMAIN="mydomain"
PUBLIC_KEY="GBE7L26OEUB2ATMEZNUSW3WSIYL62CVH5TOXINLAO6SLRGFXL7ZJCHTG"
ADDRESS="aws2"
HISTORY="curl -sf aws2_nginx/vs/{0} -o {1}"

[[VALIDATORS]]
NAME="aws3"
HOME_DOMAIN="mydomain"
PUBLIC_KEY="GBPGX4PH34Q23KFFBRBN23JN3R56QEXFCNZE6ZTB3RGPU5RIFQVL4H44"
ADDRESS="aws3"
HISTORY="curl -sf aws3_nginx/vs/{0} -o {1}"


[HISTORY.vs]
get="cp /history/vs/{0} {1}"
put="cp {0} /history/vs/{1}"
mkdir="mkdir -p /history/vs/{0}"

And here's the CaptiveCore configuration from Horizon:

UNSAFE_QUORUM=true
FAILURE_SAFETY=0
PEER_PORT=11725

[[HOME_DOMAINS]]
HOME_DOMAIN="mydomain"
QUALITY="MEDIUM"


[[VALIDATORS]]
NAME="aws1"
HOME_DOMAIN="mydomain"
PUBLIC_KEY="GB6DMQJAGCSMHTYXAO55MVI6PHQO3XPQC5TSH6APCGIKEKPVWSVILUCG"
ADDRESS="aws1"
HISTORY="curl -sf aws1_nginx/vs/{0} -o {1}"

[[VALIDATORS]]
NAME="aws2"
HOME_DOMAIN="mydomain"
PUBLIC_KEY="GBE7L26OEUB2ATMEZNUSW3WSIYL62CVH5TOXINLAO6SLRGFXL7ZJCHTG"
ADDRESS="aws2"
HISTORY="curl -sf aws2_nginx/vs/{0} -o {1}"

[[VALIDATORS]]
NAME="aws3"
HOME_DOMAIN="mydomain"
PUBLIC_KEY="GBPGX4PH34Q23KFFBRBN23JN3R56QEXFCNZE6ZTB3RGPU5RIFQVL4H44"
ADDRESS="aws3"
HISTORY="curl -sf aws3_nginx/vs/{0} -o {1}"

Output from http-command info:

  "info" : {
      "build" : "stellar-core 18.0.4 (906e866ed5ae8370da3cfde884d811812a6cec62)",
      "ledger" : {
         "age" : 1,
         "baseFee" : 100,
         "baseReserve" : 100000000,
         "closeTime" : 1635167863,
         "hash" : "e915693f1161ab9b60e258cd1c4e43a710898b6b2ae9a4c4a0dd86d9f0946004",
         "maxTxSetSize" : 100,
         "num" : 137,
         "version" : 0
      },
      "network" : "Standalone Network ; February 2017",
      "peers" : {
         "authenticated_count" : 2,
         "pending_count" : 0
      },
      "protocol_version" : 18,
      "quorum" : {
         "node" : "GB6DM",
         "qset" : {
            "agree" : 3,
            "cost" : 6656,
            "delayed" : 0,
            "disagree" : 0,
            "fail_at" : 2,
            "hash" : "4ad9c0",
            "lag_ms" : 19,
            "ledger" : 136,
            "missing" : 0,
            "phase" : "EXTERNALIZE",
            "validated" : true
         },
         "transitive" : {
            "critical" : null,
            "intersection" : true,
            "last_check_ledger" : 2,
            "node_count" : 3
         }
      },
      "startedOn" : "2021-10-25T13:05:56Z",
      "state" : "Synced!"
   }
}

Horizon info:

"horizon_version": "2.10.0-e667e8811a8033ac6682ccb597c1087c8b8d1725",
  "core_version": "stellar-core 18.0.4 (b08d3f6750bebd0b8a722354832ee8ef4682c0da)",
  "ingest_latest_ledger": 90,
  "history_latest_ledger": 90,
  "history_latest_ledger_closed_at": "2021-10-25T14:13:29Z",
  "history_elder_ledger": 2,
  "core_latest_ledger": 90,
  "network_passphrase": "Standalone Network ; February 2017",
  "current_protocol_version": 0,
  "core_supported_protocol_version": 18

I can use horizon in stellar.laboratory and every get request works fine. If I try to POST a transaction I receive this error:

curl -X POST -F 'tx=AAAAAgAAAABzdv3ojkzWHMD7KUoXhrPx0GH18vHKV0ZfqpMiEblG1gAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAJVnRioWjUDshn7VXRqMh+cYudVrWPaJe3kTIixMFPQAAAABIHyKAAAAAAAAAAAERuUbWAAAAQNiO+/NMPoE9i1kkUothICLTiic+15dUniW/vaPUkPKOCUGlxcXeivYs1cS9x6ECOvL3anf1UhEcYATypScMTwA=' 'http://localhost:8000/transactions'

{
  "type": "https://stellar.org/horizon-errors/transaction_failed",
  "title": "Transaction Failed",
  "status": 400,
  "detail": "The transaction failed when submitted to the stellar network. The `extras.result_codes` field on this response contains further details.  Descriptions of each code can be found at: https://developers.stellar.org/api/errors/http-status-codes/horizon-specific/transaction-failed/",
  "extras": {
    "envelope_xdr": "AAAAAgAAAABzdv3ojkzWHMD7KUoXhrPx0GH18vHKV0ZfqpMiEblG1gAAAGQAAAAAAAAAAQAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAJVnRioWjUDshn7VXRqMh+cYudVrWPaJe3ksTIixMFPQAAAABIHyKAAAAAAAAAAAERuUbWAAAAQNiO+/NMPoE9i1kkUothICLTiic+15dUniW/vaPUkPKOCUGlxcXeivYs1cS9x6ECOvL3anf1UhEcYATypScMTwA=",
    "result_codes": {
      "transaction": "tx_not_supported"
    },
    "result_xdr": "AAAAAAAAAGT////0AAAAAA=="
  }
}

There's no documentation about this and these solutions didn't work for us:

• first

• second (our nodes are already up to date)

We are out of ideas. Can anyone help us? Thanks