I'm not sure what is causing the problem on your app however personally I would not recommend you buy anything on apps as some can be scammy. Instead I would recommend you get your own personally wallet like a Ledger or a Trezor. However if you are looking for a free software option rather than a hardware one I would recommend Exodus as it is safe and easy to transfer between coins.
Once you set up your wallet in order to get EOS you will need a more popular coin like Bitcoin or Litecoin to transfer from. If you don't have any of these coins you will need to buy some at an exchange. For buying crypto through fiat currency like dollars the two I recommend are Coinbase or Local Bitcoin .
Once you buy it you can transfer it to your Exodus wallet and exchnage it to EOS :) Its a bit of a long process however once you practice it will become really easy. Hope this helps you out!