You have created an internally-processed network activity, and assigned a work center and the work.

Planned costs are calculated for internally-processed network activities based on the formula for costing in the work center, the activity output price for the activity type and cost center assigned to the work center, and the duration of the activity. If any of these factors are missing or incorrect, no planned costs will be displayed. The Determine Costsindicator in the network header also controls whether planned costs are calculated or not. If it is not set, no planned costs will be displayed. Reference:https://help.sap.com/doc/0f069b2e08b748f1b480d4c8b46c3c49/100/en-US/6a7a9f0a6e421014e10000000a174cb4.html