In Ni no Kuni Cross Worlds, you have a chance to get equipment, pets and skins by spending money but if you don't feel like to use your money on them then you have another option to get them by using coupons.
Of course, you can always buy the coupons in the game store but you can also get them for free with the activities listed below:
Complete your Pet Codex
Complete the Adventure Log with Monster Soulstones
Complete the weekly missions of the game
Participate in the Labyrinth of Dreams
You can also find some from the Traveling Merchant