Voicepaper uses Apple's voice engine. Unfortunately, according to Apple's policy, the generated voice can only be used for personal use and not for commercial purposes.
*From version 2.8.4, we have experimentally added a voice file creation feature using ChatGPT. The voices created with this feature can be used freely for commercial purposes. Since this is still a test version, if you would like to use this feature more extensively, please make a request through feedback.