Problem creating custom measure with dynamic_fields api parameter

Hi! I’m having some trouble creating a custom measure via the Looker API (4.0). Technically, I’m using the JavaScript SDK via extension framework, but I get the same results via standalone API as well.

I’m trying to make a new custom measure based on an existing dimension, but the measure needs to be of type number. However, these are the only types of measure I seem to be able to create (screenshot from the custom fields user interface below)

Trying to pass type number into the dynamic_fields parameter (the API way to create custom fields) and it fails. It just gives up and makes my custom field a dimension instead of a measure (no errors communicated to me)

  1. Why are these the only measure types I can create?
  2. How can I create a custom measure of type number?

Thank you! I know you’re all super busy, but it would really help me out to have some clues here.

(relevant documentation: https://docs.looker.com/exploring-data/adding-fields/custom-measure)

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