@visla allan Thanks for the question. you are trying to use the en-US-AIGenerate2Neural and en-US-AIGenerate1Neural voices with an SSML string, but these voices are not supported by the Text-to-Speech API. These voices are not listed in the list of available voices for the Text-to-Speech API.
You can find a list of available voices for the Text-to-Speech API by using the List voices method of the API.