ReqApproval workflow rule based on project PI

Summary:

Project related requisitions need to be approved by the project's PI (Principal Investigator). There is a Principal Investigator attribute but Oracle Support told me it is not valid - so I can't use it in the workflow rule. How can this rule be defined?

Content (please ensure you mask any confidential information):

Using ReqApproval task, rule defined in the HeaderHierarchyRules ruleset, tested the ReqDistributionDimension.principalInvestigstorUsername attribute (told this is not a valid attribute), tested ReqDistributionDimension.projectReserveAttr2 (didn't select the username in pjf_projects_all_b.attribute2 as the approver), tested ReqDistributionDimension.projectUserDefAttr2 (didn't select the username in pjf_projectd_allb.attribute2 as the approver). The Projects DFF was set up for pjf_projectd_all_b.attribute2 with the PI's username when we defined a similar rule for expense report approval.