How to use relation prospect_list_campaigns in API? (SugarCRM 11)

Hi,

GET http://localhost/rest/v11/ProspectLists/56991d00-3c78-11ec-8a7f-005056b0b4f5/link/prospect_list_campaigns

result is 404 with the response "Could not find a relationship named: prospect_list_campaigns"

The relation exists and with a studio filein ProspectList visible in campain and target lists relations. What is wrong or how can I activate this relation for API usage?

Regards
Harry