curl --request POST \
  --url https://app.launchdarkly.com/api/v2/flags/{projectKey} \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "clientSideAvailability": {
    "usingEnvironmentId": true,
    "usingMobileKey": true
  },
  "key": "flag-key-123abc",
  "name": "My Flag"
}
'

import requests

url = "https://app.launchdarkly.com/api/v2/flags/{projectKey}"

payload = {
    "clientSideAvailability": {
        "usingEnvironmentId": True,
        "usingMobileKey": True
    },
    "key": "flag-key-123abc",
    "name": "My Flag"
}
headers = {
    "Authorization": "<api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    clientSideAvailability: {usingEnvironmentId: true, usingMobileKey: true},
    key: 'flag-key-123abc',
    name: 'My Flag'
  })
};

fetch('https://app.launchdarkly.com/api/v2/flags/{projectKey}', 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://app.launchdarkly.com/api/v2/flags/{projectKey}",
  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([
    'clientSideAvailability' => [
        'usingEnvironmentId' => true,
        'usingMobileKey' => true
    ],
    'key' => 'flag-key-123abc',
    'name' => 'My Flag'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: <api-key>",
    "Content-Type: application/json"
  ],
]);

$response = curl_exec($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://app.launchdarkly.com/api/v2/flags/{projectKey}"

	payload := strings.NewReader("{\n  \"clientSideAvailability\": {\n    \"usingEnvironmentId\": true,\n    \"usingMobileKey\": true\n  },\n  \"key\": \"flag-key-123abc\",\n  \"name\": \"My Flag\"\n}")

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

	req.Header.Add("Authorization", "<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://app.launchdarkly.com/api/v2/flags/{projectKey}")
  .header("Authorization", "<api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"clientSideAvailability\": {\n    \"usingEnvironmentId\": true,\n    \"usingMobileKey\": true\n  },\n  \"key\": \"flag-key-123abc\",\n  \"name\": \"My Flag\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://app.launchdarkly.com/api/v2/flags/{projectKey}")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"clientSideAvailability\": {\n    \"usingEnvironmentId\": true,\n    \"usingMobileKey\": true\n  },\n  \"key\": \"flag-key-123abc\",\n  \"name\": \"My Flag\"\n}"

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

{
  "name": "My Flag",
  "kind": "boolean",
  "key": "flag-key-123abc",
  "_version": 1,
  "creationDate": "1494437420312",
  "variations": [
    {
      "_id": "e432f62b-55f6-49dd-a02f-eb24acf39d05",
      "value": true
    },
    {
      "_id": "a00bf58d-d252-476c-b915-15a74becacb4",
      "value": false
    }
  ],
  "temporary": true,
  "tags": [
    "example-tag"
  ],
  "_links": {
    "parent": {
      "href": "/api/v2/flags/my-project",
      "type": "application/json"
    },
    "self": {
      "href": "/api/v2/flags/my-project/my-flag",
      "type": "application/json"
    }
  },
  "experiments": "{\"baselineIdx\": 0,\"items\": []}",
  "customProperties": "{\"jira.issues\":{\"name\":\"Jira issues\",\"value\":[\"is-123\",\"is-456\"]}}",
  "archived": false,
  "description": "This flag controls the example widgets",
  "includeInSnippet": true,
  "clientSideAvailability": "{\"usingMobileKey\":true,\"usingEnvironmentId\":false}",
  "maintainerId": "569f183514f4432160000007",
  "_maintainer": {
    "_links": {
      "self": {
        "href": "/api/v2/members/569f183514f4432160000007",
        "type": "application/json"
      }
    },
    "_id": "569f183514f4432160000007",
    "role": "admin",
    "email": "ariel@acme.com",
    "firstName": "Ariel",
    "lastName": "Flores"
  },
  "maintainerTeamKey": "team-1",
  "_maintainerTeam": {
    "key": "team-key-123abc",
    "name": "Example team",
    "_links": {
      "parent": {
        "href": "/api/v2/teams",
        "type": "application/json"
      },
      "roles": {
        "href": "/api/v2/teams/example-team/roles",
        "type": "application/json"
      },
      "self": {
        "href": "/api/v2/teams/example-team",
        "type": "application/json"
      }
    }
  },
  "goalIds": [],
  "archivedDate": "1494437420312",
  "deprecated": false,
  "deprecatedDate": "1494437420312",
  "defaults": "{\"onVariation\":0,\"offVariation\":1}",
  "_purpose": "<string>",
  "migrationSettings": {
    "contextKind": "device",
    "stageCount": 6
  },
  "stale": {
    "readyForCodeRemoval": true,
    "readyToArchive": true,
    "cleanupId": "<string>"
  },
  "environments": {
    "my-environment": {
      "_environmentName": "My Environment",
      "_site": {
        "href": "/default/my-environment/features/client-side-flag",
        "type": "text/html"
      },
      "_summary": {
        "prerequisites": 0,
        "variations": {
          "0": {
            "contextTargets": 1,
            "isFallthrough": true,
            "nullRules": 0,
            "rules": 0,
            "targets": 1
          },
          "1": {
            "isOff": true,
            "nullRules": 0,
            "rules": 0,
            "targets": 0
          }
        }
      },
      "archived": false,
      "contextTargets": [
        {
          "contextKind": "device",
          "values": [
            "device-key-123abc"
          ],
          "variation": 0
        }
      ],
      "fallthrough": {
        "variation": 0
      },
      "lastModified": 1627071171347,
      "offVariation": 1,
      "on": false,
      "prerequisites": [],
      "rules": [],
      "salt": "61eddeadbeef4da1facecafe3a60a397",
      "sel": "810edeadbeef4844facecafe438f2999492",
      "targets": [
        {
          "contextKind": "user",
          "values": [
            "user-key-123abc"
          ],
          "variation": 0
        }
      ],
      "trackEvents": false,
      "trackEventsFallthrough": false,
      "version": 1
    }
  }
}

{
  "code": "invalid_request",
  "message": "Invalid request body"
}

{
  "code": "unauthorized",
  "message": "Invalid access token"
}

{
  "code": "optimistic_locking_error",
  "message": "Conflict. Optimistic lock error. Try again later."
}

{
  "code": "rate_limited",
  "message": "You've exceeded the API rate limit. Try again later."
}