If you are buying e-gacha tickets, they are normally 300 gold. You can get one per day for 100 gold, and right now, you even get a gold key as a bonus.

But you can actually buy TWO per day. You can buy one from the "One per day" tab on the shop. Subsequent purchases are not allowed.

You can then go to the gacha ticket tab on the shop and buy another e-gacha ticket for 100 gold. Subsequent purchases are 300 gold.

If the RNG gods are screwing you over on e-gacha, at least you can get an extra spin for less by using this trick.