How to use <amazon:domain="fun"> for Japanese in Polly?

I tried using the SSML sample instructions for using the amazon:domain tag, both with <voice> and no <voice> tag but Polly keeps saying that the SSML is invalid. The sample audio file uses a female voice, but in Polly "Takumi" the male voice is the only Neural one available. The instructions on developer.amazon.com says this: https://developer.amazon.com/en-US/blogs/alexa/alexa-skills-kit/2021/01/new-fun-speaking-style-for-japan