Help for designing how funds are handled on a poker website that accepts crypto?

Hi,

I'm hoping to write a poker website where people can deposit, play with, and withdraw cryptocurrencies.

My current idea is to use NowPayments as a crypto gateway that will facilitate receiving and sending crypto on the website.

When someone deposits, it would be represented as either say USD or just "poker chips" on the website, equivalent to the current value of that crypto in USD. When they withdraw, they will be withdrawing crypto, using their USD balance, at the current exchange rate of their chosen crypto.

But I'm worried that I could end up out of pocket if the value of the crypto changes significantly between them depositing and withdrawing as crypto.

For example. Say they deposit 1 monero, worth $100. A month later, they withdraw the $100. If, say, 1 monero is then worth $200, I only pay them 0.5 monero, so technically I've made money out of fluctuation in value. But say 1 monero is now worth $50, I have to pay them 2 monero. So I'll be out of pocket $50?

The reason I thought about doing it this way is I want to be able to accept and send any of the 70 cryptocurrencies that NowPayments support, and allow players to play poker with a single currency, say USD. (Or it could be an arbitrary made-up currency, e.g. simply "poker chips".)

What system can I use so that I won't be out of pocket when crypto values change, yet have a single "currency" that players play with on poker tables?

Hopefully there's someone financially more intelligent than me that has an answer to this!

Thanks!