The minimum amount that can be staked is 0.50 USD or in equivalent to the token you will use to place a bet.
Example scenario:
You want to place a bet with BTC token. You will then have to enter the amount of the BTC token which is equivalent to 0.50 USD or higher, since 0.50 USD is the minimum.
With the prices of the said token when this article was written, the minimum amount of BTC which you can spend to place a bet is 0.000026 BTC.
Cryptocurrency token converters are available online to be used; however, be sure that you are checking a reliable and legit websites.
(Screenshot above was taken from CoinMarketCap)