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Is the bep20 network of binance a good idea or will the transaction costs here also be too large for the concept I would like to implement?
The problem with those networks is even though the value is the same in the Exchange,
your customers will be limited since technically, it's not related to Bitcoin and [BTC] holders can't send nor receive from your app's Binance chain bitcoin [BTCB].
I agree with the above, a number of payment options will be a good feature.
If you can implement lightning payments into your app, that'll be a great.