Depending on where you park, there may be restrictions on how long you are able to park for? Any parking restrictions should be clearly displayed on local signage.
If there is a parking restriction and you have a current session that is already booked for the maximum time allowed, i.e. 4 hours or 7 days, then when you call the service again to attempt to extend the session, RingGo will prevent you from being able to do so due to these restrictions set by the parking operator.
What RingGo won't necessarily do during the second call, is stop you from creating a new session as perhaps you are parking a different vehicle or have changed location. This can lead to purchasing multiple parking sessions that overlap each other in terms of time.