Hello there,
I’m using QBcore and qb-ambulancejob for the EMS. Right now I am looking to disable the self check in from the players to the hospital (By paying and healing automaticly) if there are EMS on service.
Does anybody have an Idea on how to get this feature or if it is even possible to do it? Thank you.
Anything is possible. you would need to look for the checkin code and you could do something like create a count variable and make it track the amount of ems on duty if the count is >= 1 then you could disable the that feature. 
Thanks, but do you know where should I add the checking? I have tried in two places but it isn’t working
Depends how you tried to do it 
I tried to put the counter using the Doctorcount function but I can’t get it to work in any function, do you know in which function do I need to introduce the counter?