It sounds that easy and it should be that easy...but I don't get the solution...
To make it simple: I'm searching exact this solution in SugarCRM like it is described at SFDC.
--> https://help.salesforce.com/articleView?id=faq_campaigns_how_can_i_add_contacts.htm&type=5
(To add an individual contact or lead to a campaign, click Add to Campaign on the contact or lead record, and then select a campaign.)
Is there a similar function in Sugar?
