How to handle usage limits when using n8n workflows as API endpoints?

If we use n8n workflows like API endpoints for a SaaS or client app how do we control usage by SaaS application plan? For example Basic SaaS plan users get 30 workflow runs per day and Pro users get 100 etc.. Do you manage this inside n8n or in your app backend with custom logic or through an API gateway? Trying to understand what works well and what becomes difficult at scale