App supports multiple currency but depends on Theme to provide necessary details around currency format to the app, for example theme must provide money_format information and formatMoney function which app can use to format the currency correct.
Adding support to your theme
Shopify.formatMoney function is availble in Shopify's optionselector script,
How to Include option_selection.js in theme.liquid?
If after adding option_selection, App is still not dsiaplying currency format correctly then most likely theme is not providing money_fromat correctly, app is looking for money format information in following order:
If you are using a thrid party theme then please contact theme developer, if you are using Shopify free theme and in an unlikely scenario of currency format still not showing correctly then please contact support.