Dokka takes the currencies from the company settings and the account settings (per the supplier that was chosen in the invoice entry screen).
If the currency isn't set up at all or not set up correctly, Dokka will only show the main currency and the secondary currency that are set up in SAP for that company.
If the currency doesn't show up, first check if it is set up correctly in the Currency Settings screen:
If the currency is set up correctly in this screen but still won't show up, check if the currency is set up correctly for this specific account:
Once you've set it up, click the Force ERP Synchronization in Dokka: