public function validateCall(): void
    {

        if (! in_array($this->method, ['get', 'post', 'put', 'patch', 'delete']))
            throw new Exception('Invalid HTTP method used');

        if (trim($this->endpoint) === '')
            throw new Exception('Empty endpoint used');

        // Enfore a version specification unless this is a 'meta' call.
        if (trim($this->version) === '' && ! (in_array('meta', $this->tags())))
            throw new Exception('Version is empty');
    }