Unable to complete initial configuration due to form error.

The site_id field uses the "machine_name" form element. I presume to ensure proper characters are used.

The "machine_name" element also requires a check for duplicate machine names and this form does not provide a callback for this. What would it check for duplicates?

I think this may be the wrong field type to use for this. If we are only concerned with ensuring proper name format, it's better to check with field validation and provide a helpful error message.

I've attached a patch that changes the field type to "textfield", adds helpful instruction in the field description, and validates to ensure only letters, numbers, hyphens and underscores are used.

If I'm misunderstanding the purpose of using the machine name element here, please let me know.

I had the same issue and the patch fixed it.