KickBack RKC

Use instead of using 4NT using the lowest impossible bid above the 4th level of that suit is RKC

The RKC is 30-14 and NOT 1430

Clubs - 4♦ - Asking RKC for Clubs

Diamonds - 4♥ - Asking RKC for Diamonds

Hearts - 4♠ - Asking RKC for Hearts

Spades - 4NT - Asking for RKC for Spades

This is once a suit is agreed on, if there is a fight between suits then follow two rules

If you can bid your suit at a lower level without losing anything then it is RKC (example: 1H-2D(GF)-2H-3D-4H is RKC for diamonds because you can bid 3H without losing anything)
If you haven't agreed on a suit than the lower of the impossible suits is for the lower suit and second lowest impossible is the higher suit (1H-2D(GF)-2H-3D-3H) In this case 4 Hearts is to play so 4S is RKC for diamonds and 4NT is RKC for hearts

In most auctions when Kickback RKC is available this opens up 4NT as a quantitative raise