This must be a JSON encoded string that would typically be fetched from the JS API:
piwikTracker.getAttributionInfo() and that you have JSON encoded via JSON2.stringify()
If you call enableCookies() then these referral attribution values will be set
to the 'ref' first party cookie storing referral information.
public setAttributionInfo ( string $jsonEncoded ) | ||
$jsonEncoded | string | JSON encoded array containing Attribution info |