I am planning to use the Google Text-to-Speech API for commercial purposes. I will not generate more than 25,000 characters per month. In this case as I know I can use it for free and I don’t need to obtain a commercial license or give credit to Google, am I correct?
Unlike Translate, Text-to-Speech does not have attribution requirements. You can use the audio data files you create using Text-to-Speech in your applications or media in compliance with the Google Cloud Platform Terms of Service including compliance with all applicable law. [source] Hope that helps!