Delete previous filled in value after getting an error message

Hello people,  I have a question regarding my Mendix application.  I made a microflow which checks if a date or a room already has been booked. If it has been booked i get an error message, as I want. After getting that error message when i click on  'Ok' the value is still filled.  As seen above i get the error message, i then proceed to press 'Ok'  and see this view: The room(ruimte) which was already filled(ACDPL.6.560) should be empty after my microflow saw that it was booked. It still stays filled and I can even save the reservation despite it being full.  I hope you guys have any tips for me on how to solve this. Kind regards, 
1 answers

Guess you have an on change microflow on the room selector.

In that case, you can do the following: 

In this on change microflow, add a change activity after the availability check, in the 'false' sequence flow.
Change the object of the roombooking (context object)  and change the member booking_Room (association between the context object and the room object. Set value empty.  And refresh the object in the change activity