Add the Glowing: option under the Lore: option. Here is an example:
Code (Text):
RankUp:
Item: '331'
Name: '&8&l>&7&l>&c%Arg% Voucher&7&l<&8&l<'
Lore:
- '&7Use this voucher to rank up to &c%Arg%&7.'
- '&7&l(&6&l!&7&l) &7Right click to redeem.'
Glowing: true
Commands:
- 'pex user %Player% group set %Arg%'