Hello and welcome to the Forum!

On the screenshot above I see that you have equipped your Champion Elhain with  6 offense Artifacts, but you haven't Upgraded them to Level 4 or higher. And it shows 3/6 completed because you have equipped some other Rare ATK type Champion with 3 Offense Artifacts of Level 4 or higher. Thus, the mission will be completed right after you Upgrade at least 3 more the Offense Artifacts on Elhain to Level 4 or higher.

jorgeottajunior said:

I just can't seem to get it right. Mission is: Equip a rare ATK type Champion with 6 offense Artifacts of Level 4 or higher

Screenshot below shows what I think is right. Why it is only 3/6?

Thanks in advance