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.
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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)