not working normally

I bought your this plugin for another site a year ago and it worked fine for the exact function I needed!

I have a plugin, on another site of the old version and the function normally does!
I have several currencies and I want, when the customer chooses a currency on the site, at the end he finishes (on the page checkout) for the currency I need, as my bank accepts only one currency!
for example, a product costs $ 50, I want it to end up on that currency with my credit card at the end
$ 50 = 25000AMD
and now $ 50 = 50AMD