Hello,
You need to use a multidimensional array:
$textData->addText(array(array('text' => $bullet['text']['data'], 'underline' => 'single')));
Or a string:
$textData->addText($bullet['text']['data'], array('underline' => 'single'));
But not a single array as you are using to add text to the WordFragment. A multidimensional array is needed to be able to add texts with different properties:
$textData->addText(
array(
array('text' => $bullet['text']['data'], 'underline' => 'single'),
array('text' => ' Other text', 'bold' => true),
)
);
Regards.