phacility/phabricator · error · Exception

In this poll, you may only vote for one option.

Error message

In this poll, you may only vote for one option.

What it means

PhabricatorSlowvoteVoteController throws this when a submitted ballot contains more than one selected option on a plurality (single-choice) poll ($is_plurality with count($votes) > 1). The stock UI renders radio inputs for such polls, so hitting this means a modified/hand-crafted POST, a custom client, a browser extension duplicating form fields, or a customized template rendering checkboxes for every poll.

Source

Thrown at src/applications/slowvote/controller/PhabricatorSlowvoteVoteController.php:54

    $method = $poll->getMethod();
    $is_plurality = ($method == SlowvotePollVotingMethod::METHOD_PLURALITY);

    if (!$votes) {
      if ($is_plurality) {
        $message = pht('You must vote for something.');
      } else {
        $message = pht('You must vote for at least one option.');
      }

      return $this->newDialog()
        ->setTitle(pht('Stand For Something'))
        ->appendParagraph($message)
        ->addCancelButton($poll->getURI());
    }

    if ($is_plurality && count($votes) > 1) {
      throw new Exception(
        pht('In this poll, you may only vote for one option.'));
    }

    foreach ($votes as $vote) {
      if (!isset($options[$vote])) {
        throw new Exception(
          pht(
            'Option ("%s") is not a valid poll option. You may only '.
            'vote for valid options.',
            $vote));
      }
    }

    $poll->openTransaction();
      $poll->beginReadLocking();

      $poll->reload();

View on GitHub (pinned to 5720a38cfe)

Solutions

1. Submit exactly one option ID for plurality polls
2. If you customized poll templates, render single-choice inputs (radio behavior) for plurality polls and multi-select only for approval polls
3. If this fires from normal UI use, check for browser extensions or scripts duplicating the votes[] fields

Example fix

# before: multiple selections on a single-choice poll
curl -b cookies -d "votes[]=101&votes[]=102" https://phab.example.com/V1/vote/

# after: one selection
curl -b cookies -d "votes[]=102" https://phab.example.com/V1/vote/

// Client-side, before POSTing a ballot
if (poll.isPlurality && selectedOptionIds.length > 1) {
  // block submit: single-choice polls accept exactly one option
}

When it happens

Trigger: POSTing to a poll's vote endpoint (e.g. /V<id>/vote/) with two or more values in the votes[] fields on a poll configured for a single choice. Note empty ballots are handled earlier by a dialog; this check runs before per-option validation.

Common situations: Automated voting scripts; replayed/edited form submissions; template customizations that render checkboxes regardless of poll method; duplicated form fields from extensions or markup changes.

Related errors

• Request includes restricted parameter "%s", but this control
• Unrecognized verb: %s
• Invalid revision ID "%s".
• Failed to decode rule data.
• Too many relationships (%s, of type "%s").

AI-assisted analysis of phacility/phabricator@5720a38cfe (2026-08-21). Data as JSON: /api/errors/506ba765ed20badc. Report an issue: GitHub.