Hi @pszew93
You need to check 2 things. First check if eVar0 is firing on the order confirmation page and second is to check the campaign "expiration" settings under admin console. Please use the link below for more details on how to check for the expiration setting:
https://experienceleague.adobe.com/docs/analytics-learn/tutorials/administration/manage-report-suite...
Also if in case you want to stitch campaign variable with each order then set the expiration setting as "purchase" event so that the campaign variable will persists until a purchase had been made.