Can we have serial and parallel approval rule for same stage in Requisition Approval Rule

Currently as per Business Requirements, we have multiple BU's wherein in one particular BU the approval flow is serially and for other BU the approval flow is parallely. We need both Serial and Parallel Routing in Header Stage for Requisition Approval Rule.

However, once the setup is done and requisition is created, we click on 'Manage Approval' and below message is received -

"The approval history can't be displayed because this task couldn't be assigned to any approver. Details Ruleset did not return any results. Reconfigure the conditions in the rule set HeaderStageFirstResponderWinsRules for the task ReqApproval so that approvers are found. Model the ruleset so that it returns a list builder specification."