It seems that you get the same error as Rigify Generate Rig Error Index 0 Out of Range 2.83

Quoting blr's answer:

In order for the Rigify Generate button to work, the option in Preferences > Editing > Objects > Duplicate Data > Armature must be checked.

EDIT

It seems that you get the same error as Rigify Generate Rig Error Index 0 Out of Range 2.83.

blr's answer should help you