Hi, @selvadev13 .
Which region is your client’s store operating from? If located in an eligible region, are they using Shopify Payments as a payment provider on their store?
The reason that I ask is because currently, Shopify Payments is a requirement for stores wanting to allow customers to checkout in multiple currencies. If your client is based in a region that isn’t currently supportable by Shopify Payments, they will need to use a third-party payment provider, which means that all orders will then be processed in the store’s default currency. There isn’t a workaround for this I’m afraid, this is currently a limitation of our Shopify Markets feature as explained in this guide.
In the meantime, we encourage users to explore a range of currency converter apps on our Shopify App Store here. It’s important to keep in mind that these apps will mostly just display a different currency to customers up until checkout, so customers are still required to checkout in the store’s default currency if Shopify Payments isn’t present and active. If you’d like to explore this option further though, I recommend starting with this currency converter app, and this one to begin with to see if they’ll suit your client’s needs.