Silver Rant

Has anybody faced the issue of having a lot of parts but no silver to upgrade planes? It's quite frustrating after a point. I have planes that I sometimes play but love can can level up till 13-14 maybe but I am stuck because of silver.

The Devs should give an option of buying it with money maybe in the game. Itself. I am from India and is a bit sceptical regarding purchase made on its website. I see no option of getting them through INR. So I have to get to a PayPal account which I don't have.

Need some suggestions please.