Hey there, 'Requirement not Met' only refers to the ability to refund a purchased mod. The same rules that govern mod purchase also applies to mod refunding - you have to have three mods in column 1 to be able to purchase one in column 2 - meaning if you've purchased a mod in column 2, you can't refund a column 1 mod if it would take you down to less than three. In this case, 'Requirement Not Met' will be displayed. In your case, you do have four in column 1, but refunding 1 would mean you do not have 10 across columns 1-4 so here it's column 5 locking everything in, in earlier columns. Refund both column 5 mods, note that the restriction on your other mods will disappear. Then refund one of column 1's mods to see it reappear on the other column 1 mods. This does not affect mod function in any way. Which champion mods are not working? Exotic weapons especially may have a keyword ability that classifies them as a specific type of anti-champion weapon; this both includes text like 'strong against X champion' like Arbalest, but also even having things like Slow, or Jolt, will also do this. Weapons that do either, cannot gain the effect of an anti-champion mod. One recent case is Wicked Implement's 'slow' which locks it into being anti-Overload, and so cannot get the benefit of anti-barrier Scout Rifle.