Seldaek/monolog · error · InvalidArgumentException

Could not resolve message as instance of Email or a callable

Error message

Could not resolve message as instance of Email or a callable returning it

What it means

Error "Could not resolve message as instance of Email or a callable returning it" thrown in Seldaek/monolog.

Source

Thrown at src/Monolog/Handler/SymfonyMailerHandler.php:85

    /**
     * Creates instance of Email to be sent
     *
     * @param string      $content formatted email body to be sent
     * @param LogRecord[] $records Log records that formed the content
     */
    protected function buildMessage(string $content, array $records): Email
    {
        $message = null;
        if ($this->emailTemplate instanceof Email) {
            $message = clone $this->emailTemplate;
        } elseif (\is_callable($this->emailTemplate)) {
            $message = ($this->emailTemplate)($content, $records);
        }

        if (!$message instanceof Email) {
            $record = reset($records);

            throw new \InvalidArgumentException('Could not resolve message as instance of Email or a callable returning it' . ($record instanceof LogRecord ? Utils::getRecordMessageForException($record) : ''));
        }

        if (\count($records) > 0) {
            $subjectFormatter = $this->getSubjectFormatter($message->getSubject());
            $message->subject($subjectFormatter->format($this->getHighestRecord($records)));
        }

        if ($this->isHtmlBody($content)) {
            if (null !== ($charset = $message->getHtmlCharset())) {
                $message->html($content, $charset);
            } else {
                $message->html($content);
            }
        } else {
            if (null !== ($charset = $message->getTextCharset())) {
                $message->text($content, $charset);
            } else {
                $message->text($content);

View on GitHub (pinned to 57eb102834)

When it happens

Trigger: Thrown at src/Monolog/Handler/SymfonyMailerHandler.php:85 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Seldaek/monolog@57eb102834 (2026-08-17). Data as JSON: /api/errors/7bd99545fe55ed58. Report an issue: GitHub.