Veteran's Chest - How to open?

I received a "Veteran's Chest" recently, however, I can't seem to open it. How do you open the this chest?

I can see the Open the chest button, but clicking it simple results in a message by Misty: "You can only open the chest once you earn an additional SG in games after 2020-06-12."
But, how many SGs, is just one enough ("an additional SG")? Which games? Gamehag site, or some specific game?

Has anyone managed to open it yet?

In order to open this chest, you need to collect at least 100 SG from the time you last opened a promotional chest. thats what mine says

Thanks jesse12341, now I feel even more confused:
1 - how come it says different things for us?
2 - which chests are considerd "promotional chest"?
3 - I have collected more than 100 SGs since I last opened ANY chest, yet I can't open it

Hey guys, let me solve your issue.

VETERAN'S CHEST is a special reward for completing all 3 full tasks of the new event of Gamehag (Great Battle). So, we can not open it unless we perfectly complete all of them. The reason we see this "Error" is: A simple incorrect message which should be fixed by the GH team. If you want to know more about this event check it here:

Gamehag.com/lp/gaijin