The function to use an existing race as a template for homebrew is not currently work. Have used it plenty of times before. Now it simply gives the "Contact Support" message.

Which race?

Happened on multiple races but upon further testing it seems to be the Monsters of the Multiverse races especially.

I wonder if it’s anything to do with this: (https://www.dndbeyond.com/forums/d-d-beyond-general/bugs-support/159780-homebrew-subclass-based-on-lunar-not-possible).

Still receiving the same 500 error.

Any update on this bug? Again several of the MotM races can't be used for homebrew templates. For example none of the Genasi. Still get the Internal Server Error 500.

I'm experiencing the same thing. I want to use the spellcasting from Air Genasi as a template for a new race bc idk how to make it so I can choose Int, Wis, or Cha as the spellcasting stat. None of the MotM races work as templates, though. It just crashes immediately.

Quote from YourBoiCyan >>

I'm experiencing the same thing. I want to use the spellcasting from Air Genasi as a template for a new race bc idk how to make it so I can choose Int, Wis, or Cha as the spellcasting stat. None of the MotM races work as templates, though. It just crashes immediately.

 
There are instructions on how to accomplish that in the Homebrew Subclasses & Species FAQ #17: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).