Today we have the 3 parts required to summon the boss in Mechagon but it appears that the two side bars are not interactable and the boss is not summonable at this time.
This is currently being looked into.
You can find more known issues in our forum post:
i lost my item for the summon how can i go about getting it back
at this moment on Shu’halo the two pylons on the left and right are activated and the middle is not working you can click on it but nothing happens after the cast and the noise happens
You would need to file a bug report.