GROHE flush not working properly

[BotusBuild]

As you know I got the GROHE frame and pan installed, but it seems the flush does not want to work. You have to keep the buttons pressed in for the water to flow. Basically the release valve (correct term?) was not engaging.

First picture shows the top of the release valve on the left, and a part of the refill/float mechanism to the right.

The second picture shows where the top of the release valve should get to when a flush button is pressed.

 

  

 

But, it is catching as per the next photo

 

I've tried "twisting" these two apart but hard plastic don't give.

 

Question - cut the top of the release valve (enough to allow it to rise properly), or cut the alternative installation slot and that "flange"?

 

Othe photos 

  

Edited 3 hours ago by BotusBuild