You can use Admin endpoints to define the secondary currency for a site by setting the secondaryCurrency
property.
To associate secondary currency to a site, issue a PUT request to the /ccadmin/v1/sites/{site_id}
endpoint on the administration server. The following example identifies the secondary currency of the Site US as US Dollars:
PUT/ccadmin/v1/sites/siteUS
{ "properties": [ { "secondaryCurrency": "USD", } }