Let's say your Flask app has the following route.

@app.route("/api/v1")
def apiv1():
  return "hello world"

And when requesting /api/v1 (without the trailing slash) a 308 Redirect is being returned. On the other hand, requesting /api/v1/ (with the trailing slash) returns "hello world" in the route.

This happens because Flask uses werkzeug.routing.Rule which sets strict_slashes to True. With this configuration, the trailing slash must be included. If you want to allow requests without the trailing slash, set strict_slashes to False.

@app.route("/api/v1", strict_slashes=False)
def apiv1():
  return "hello world"