Hello, I solved this mission with some hints. Here I report a point to improve on the mission introduction.

The introduction says:

Your mission is to figure out which country opens your emails the most.

But, this is also said:

Output: String, Two-digit country code of country that has more unique clicks.

Actually, this is confusing because there exists both opens and unique_clicks in the response.

Thus, I suggest to change the introduction message such as:

Your mission is to figure out which country has most unique clicks to your emails.