That happens if you are using the free version on Ngrok. You could also check out zrok.io, its an open source alternative I work on. We also have a free SaaS version for easy usage.
The real game changer (but may not be relevant you) is zrok is being abled to use the OpenZiti SDKs so that you can embed zrok functions directly into an application. We have built the Go one so far, but all others will be done in due course.