task.item.addfile

curl -X POST \
-H "Content-Type: application/json" \
-H "Accept: application/json" \
-d '{"TASK_ID":"140","FILE":{"NAME":"desc.txt","CONTENT":"BASE64_ENCODED_CONTENT_OF_DESC.TXT"},"auth":"z3eamwwkpgl7u18kx14q1s4c0ffckqsn"}' \
https://**put_your_bitrix24_address**/rest/task.item.addfile

// This snippet is an ES module: top-level await requires type="module" or a bundler.
// $b24 is an already-initialized SDK instance (see the SDK "Get started" guide).
import { Text } from '@bitrix24/b24jssdk'
import type { B24Frame } from '@bitrix24/b24jssdk'

declare const $b24: B24Frame

// TODO: verify API version — the page does not show a JSON response example
// Shape of the payload returned in result (ID of the uploaded file)
type AddFileResult = number

try {
  const response = await $b24.actions.v2.call.make<AddFileResult>({
    method: 'task.item.addfile',
    params: {
      TASK_ID: '140',
      FILE: {
        NAME: 'desc.txt',
        CONTENT: 'BASE64_ENCODED_CONTENT_OF_DESC.TXT',
      },
    },
    requestId: Text.getUuidRfc4122()
  })

  // The payload is available only on a successful response
  if (!response.isSuccess) {
    console.error(response.getErrorMessages().join('; '))
  } else {
    const result = response.getData()!.result
    console.info('Uploaded file ID:', result)
  }
} catch (error) {
  // Thrown on transport or SDK failures (AjaxError, SdkError, etc.)
  console.error(error)
}

<!-- Load the SDK (UMD build); it is exposed as the global B24Js -->
<script src="https://unpkg.com/@bitrix24/b24jssdk@1/dist/umd/index.min.js"></script>
<script>
  async function addFileToTask() {
    try {
      // Initialize the SDK inside a Bitrix24 frame
      const $b24 = await B24Js.initializeB24Frame()

      const response = await $b24.actions.v2.call.make({
        method: 'task.item.addfile',
        params: {
          TASK_ID: '140',
          FILE: {
            NAME: 'desc.txt',
            CONTENT: 'BASE64_ENCODED_CONTENT_OF_DESC.TXT',
          },
        },
        requestId: B24Js.Text.getUuidRfc4122()
      })

      // The payload is available only on a successful response
      if (!response.isSuccess) {
        console.error(response.getErrorMessages().join('; '))
        return
      }

      const result = response.getData().result
      console.info('Uploaded file ID:', result)
    } catch (error) {
      // Thrown on transport or SDK failures (AjaxError, SdkError, etc.)
      console.error(error)
    }
  }

  document.addEventListener('DOMContentLoaded', addFileToTask)
</script>

try {
    $response = $b24Service
        ->core
        ->call(
            'task.item.addfile',
            [
                'TASK_ID' => '140',
                'FILE'    => [
                    'NAME'    => 'desc.txt',
                    'CONTENT' => 'BASE64_ENCODED_CONTENT_OF_DESC.TXT',
                ],
            ]
        );

    $result = $response
        ->getResponseData()
        ->getResult();

    if ($result->error()) {
        error_log($result->error());
        echo 'Error: ' . $result->error();
    } else {
        echo 'Success: ' . print_r($result->data(), true);
    }

} catch (Throwable $e) {
    error_log($e->getMessage());
    echo 'Error adding file to task: ' . $e->getMessage();
}

BX24.callMethod(
    "task.item.addfile",
    {
        TASK_ID: "140",
        FILE: {
            NAME: "desc.txt",
            CONTENT: "BASE64_ENCODED_CONTENT_OF_DESC.TXT"
        }
    },
    function(result) {
        if(result.error())
            console.error(result.error());
        else
            console.log(result.data());
    }
);

require_once('crest.php');

$result = CRest::call(
    'task.item.addfile',
    [
        'TASK_ID' => "140",
        'FILE' => [
            'NAME' => 'desc.txt',
            'CONTENT' => base64_encode(file_get_contents($_SERVER['DOCUMENT_ROOT'] .'/desc.txt'))
        ]
    ]
);

echo '<PRE>';
print_r($result);
echo '</PRE>';