curl --request POST \
  --url https://api.kas.fyi/v1/rpc/submitTransactionReplacement \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "transaction": {
    "version": 0,
    "inputs": [
      {
        "previousOutpoint": {
          "transactionId": "fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820",
          "index": 1
        },
        "signatureScript": "4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01",
        "sequence": 0,
        "sigOpCount": 1
      }
    ],
    "outputs": [
      {
        "value": "100000",
        "scriptPublicKey": {
          "version": 0,
          "script": "208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac"
        }
      }
    ],
    "lockTime": 0,
    "subnetworkId": "0000000000000000000000000000000000000000",
    "gas": "0",
    "payload": ""
  }
}
'

import requests

url = "https://api.kas.fyi/v1/rpc/submitTransactionReplacement"

payload = { "transaction": {
        "version": 0,
        "inputs": [
            {
                "previousOutpoint": {
                    "transactionId": "fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820",
                    "index": 1
                },
                "signatureScript": "4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01",
                "sequence": 0,
                "sigOpCount": 1
            }
        ],
        "outputs": [
            {
                "value": "100000",
                "scriptPublicKey": {
                    "version": 0,
                    "script": "208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac"
                }
            }
        ],
        "lockTime": 0,
        "subnetworkId": "0000000000000000000000000000000000000000",
        "gas": "0",
        "payload": ""
    } }
headers = {
    "x-api-key": "<api-key>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {'x-api-key': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    transaction: {
      version: 0,
      inputs: [
        {
          previousOutpoint: {
            transactionId: 'fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820',
            index: 1
          },
          signatureScript: '4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01',
          sequence: 0,
          sigOpCount: 1
        }
      ],
      outputs: [
        {
          value: '100000',
          scriptPublicKey: {
            version: 0,
            script: '208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac'
          }
        }
      ],
      lockTime: 0,
      subnetworkId: '0000000000000000000000000000000000000000',
      gas: '0',
      payload: ''
    }
  })
};

fetch('https://api.kas.fyi/v1/rpc/submitTransactionReplacement', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.kas.fyi/v1/rpc/submitTransactionReplacement",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'transaction' => [
        'version' => 0,
        'inputs' => [
                [
                                'previousOutpoint' => [
                                                                'transactionId' => 'fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820',
                                                                'index' => 1
                                ],
                                'signatureScript' => '4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01',
                                'sequence' => 0,
                                'sigOpCount' => 1
                ]
        ],
        'outputs' => [
                [
                                'value' => '100000',
                                'scriptPublicKey' => [
                                                                'version' => 0,
                                                                'script' => '208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac'
                                ]
                ]
        ],
        'lockTime' => 0,
        'subnetworkId' => '0000000000000000000000000000000000000000',
        'gas' => '0',
        'payload' => ''
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json",
    "x-api-key: <api-key>"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.kas.fyi/v1/rpc/submitTransactionReplacement"

	payload := strings.NewReader("{\n  \"transaction\": {\n    \"version\": 0,\n    \"inputs\": [\n      {\n        \"previousOutpoint\": {\n          \"transactionId\": \"fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820\",\n          \"index\": 1\n        },\n        \"signatureScript\": \"4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01\",\n        \"sequence\": 0,\n        \"sigOpCount\": 1\n      }\n    ],\n    \"outputs\": [\n      {\n        \"value\": \"100000\",\n        \"scriptPublicKey\": {\n          \"version\": 0,\n          \"script\": \"208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac\"\n        }\n      }\n    ],\n    \"lockTime\": 0,\n    \"subnetworkId\": \"0000000000000000000000000000000000000000\",\n    \"gas\": \"0\",\n    \"payload\": \"\"\n  }\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("x-api-key", "<api-key>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://api.kas.fyi/v1/rpc/submitTransactionReplacement")
  .header("x-api-key", "<api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"transaction\": {\n    \"version\": 0,\n    \"inputs\": [\n      {\n        \"previousOutpoint\": {\n          \"transactionId\": \"fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820\",\n          \"index\": 1\n        },\n        \"signatureScript\": \"4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01\",\n        \"sequence\": 0,\n        \"sigOpCount\": 1\n      }\n    ],\n    \"outputs\": [\n      {\n        \"value\": \"100000\",\n        \"scriptPublicKey\": {\n          \"version\": 0,\n          \"script\": \"208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac\"\n        }\n      }\n    ],\n    \"lockTime\": 0,\n    \"subnetworkId\": \"0000000000000000000000000000000000000000\",\n    \"gas\": \"0\",\n    \"payload\": \"\"\n  }\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.kas.fyi/v1/rpc/submitTransactionReplacement")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["x-api-key"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"transaction\": {\n    \"version\": 0,\n    \"inputs\": [\n      {\n        \"previousOutpoint\": {\n          \"transactionId\": \"fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820\",\n          \"index\": 1\n        },\n        \"signatureScript\": \"4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01\",\n        \"sequence\": 0,\n        \"sigOpCount\": 1\n      }\n    ],\n    \"outputs\": [\n      {\n        \"value\": \"100000\",\n        \"scriptPublicKey\": {\n          \"version\": 0,\n          \"script\": \"208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac\"\n        }\n      }\n    ],\n    \"lockTime\": 0,\n    \"subnetworkId\": \"0000000000000000000000000000000000000000\",\n    \"gas\": \"0\",\n    \"payload\": \"\"\n  }\n}"

response = http.request(request)
puts response.read_body

{
  "transactionId": "34e9538fd3225652553930657c3d767d5ccab0fcd545038a69c202e45929dcd6",
  "replacedTransaction": {
    "version": 0,
    "inputs": [
      {
        "previousOutpoint": {
          "transactionId": "fa99f98b8e9b0758100d181eccb35a4c053b8265eccb5a89aadd794e087d9820",
          "index": 1
        },
        "signatureScript": "4123c94e322fd98ce4ba8b2e33b47f2984a2f741ecfea6fb48eb90d209a46b9d58639888a1575a717cb243b006edd720a7153e9a7e63f4539958d0a44eea8bfa9f01",
        "sequence": 0,
        "sigOpCount": 1
      }
    ],
    "outputs": [
      {
        "value": "100000",
        "scriptPublicKey": {
          "version": 0,
          "script": "208b42bec57f9a538f740b067f947a5b29e04043218a37ff1fa7fb5ee850fd3fd3ac"
        }
      }
    ],
    "lockTime": 0,
    "subnetworkId": "0000000000000000000000000000000000000000",
    "gas": "0",
    "payload": ""
  }
}