We should enable bypass authentication option is disabled in agent rule to execute Activities that require Authentication to run,

According to Pega 

"In most cases, clear the check box ( Require Authentication to run)if the activity is for an agent. Agents are not true authenticated users and by default cannot run activities that are restricted to authenticated users. However, this check box is ignored by agents for which the Bypass activity authentication check box (on the Security tab is checked; they can run activities regardless of the Authenticate? value."