Bitcoin first appeared in 2008.
With more than 20 different currencies, even such as Cardano, and in on three to five cryptocurrency exchanges you definitely encounter some difficulties.
A small digression, scalability needs to include the database
Freemium and plans are best suited.
Believe me, the traders (your target audience) are willing to pay $10, $20 and even $50-$100 a month to be sure that you will receive important notification on time.
As You know, in addition to developer of mobile applications we need a back-end developer to configure the server to send notifications (Google Cloud Messaging for example).
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