Can you add a second screenshot showing the champion in question with his gear? For instance, are you sure all the gear is at level 4 - which has nothing to do with either the rarity or the number of stars it has, it's just a question of paying silver to level it up? 

Here is a screenshot of the character in question. I bumped him up to 4 stars in case that I was misreading the mission or whatnots. I’m sure I’m doing something dumb but can’t see it. Appreciate the help!

Bob the Nailer said:

Here is a screenshot of the character in question. I bumped him up to 4 stars in case that I was misreading the mission or whatnots. I’m sure I’m doing something dumb but can’t see it. Appreciate the help!

Okay, the artifacts are 4* but NOT level 4, you need to upgrade all of those artifacts up to level 4

Example:

https://i.imgur.com/ipKVLml.jpg

On my gears there a +16 or +12 on the bottom right corner of each gear, that's the level the mission is talking about.

Yours have none, meaning it hasn't been upgraded to level 4 yet