There are two types of price currencies in the app that are used in various places. The display currency and the billing currency.
The billing currency
Your billing currency is the actual currency that you are being charged, and invoiced in. You can set up your billing currency when you're adding an invoice profile. You can create multiple invoice profiles in different currencies to ensure your company needs are fulfilled. On how to set up your invoice profile, you can see it here.
The display currency
The display currency is essentially an "on-the-fly" FX conversion of the billing currency to a different one. Opposed to the billing currency, your display currency can be adjusted at any time.
For example if your billing currency is set to SGD, but you change the display currency to EUR, then you will essentially look at a converted SGD price for your booking.
Note: even if you change your display currency, you will ALWAYS be charged in the billing currency.