To work in multi currency, you will need to first create a new template using the foreign currency bookmarks on all your related Synergy documents, for example:
Credit note summary
Credit note with stage breakdown
Do this from the Organization menu > Settings > Templates > Document.
The easiest way to update the bookmarks is to create a copy of the document you want to invoice in a foreign currency and replace the existing bookmarks with the new foreign currency bookmarks.
There are over 100 foreign currency bookmarks you can use. These are clearly marked with ‘foreign currency’.