I was wondering the same. All I have found is this,
Does Wattpad have a text to speech feature?
Wattpad uses a text to speech beta feature that is included in numerous English stories. The platform analyzes and identifies TTS’ effectiveness in enhancing the Wattpad reading experience. Currently, not everyone is eligible to use it, as it is reserved for the stories for which the platform has enabled the feature.
How to enable text to speech on Wattpad?
To find all the stories with the TTS feature, users must look for the #texttospeech tag. However, the TTS feature is in the beta phase, and the platform doesnt include this feature in other stories.