Warcraft Rumble Shop


I am playing Warcraft Rumble, and is wondering about the prices ingame vs battle.net app shop.

Ingame my prices are listed as DKK (1€ = roughly 7,46DKK).
Ingame 12000coins cost 899DKK (120€)
Battle.net 12000coins cost 99.99€ (746DKK)
And sadly the battle.net app shop forces me to buy ingame, which I am also not understanding. Shouldn’t it be possible to buy from both? I am sent to the ingame shop from the battle.net app if I press purchase.

Why is that exactly? Also, why is the 12000coins more expensive than 2x 6000coins?