Good morning Elisa,
Thank you for your reply and update.
Using your information and cross-references gleaned from a GET command in the API with a Call Queue actively set for myself, I was able to discover the appropriate body setup for the JSON in this case:
Using this, I successfully updated the Business Hours missed call routing target to the desired Call Queue.
However, I want to point out, this was exceptionally difficult to figure out because the name of the properties are different in PATCH than GET (call_not_answer_action vs action, forward_to_extension_id vs forward_to), and the “routing” subsetting property is technically the top hierarchy but was not actually needed at all.
You can consider this closed/resolved.