What are prerequisites for auto posing the Metarig?

Posing the metarig requires a successful preprocess by renaming bones in the target character. See FAQ on preprocess for details.

Additionally the script is designed to work only with the default metarig as it appears when using the Add -> “Human (Meta-rig)” operator. The script relies on bone names to keep track of operations so you can not change any of the names. However you can freely add additional bones and rename them as long as the bone was not part of the original metarig or added by the script itself e.g. the twist bones etc.

A recommended workflow would be to add a new default meta-rig. Use the script to pose it and only then add additional bones if needed without touching any of the existing ones.