Hi Olaf,
have you seen already https://www.ibm.com/docs/en/wm-api-gateway-saas/11.1.0?topic=apis-monetize
It explains how that is done in API GW. We have by the way the same also for the Integration components (aka EMBED).
There the feature is called "plans": More details at: https://www.ibm.com/docs/en/wm-embed?topic=settings-plans
To go more into details / examples please see also this forum under: LINK
Best regards,
Holm.