unable to fetch value from account using account id using joinfield value

Hi Friends,

I have a simple requirement. But for some reasons it is not working as expected (only for the Account id part). I have tried different ways of syntax to accomplish this but in vain. Please see if you can provide some inputs

scenario: this is for activity object. if owner is not a specific user (2 users), then update the value from the the activity owner text field, else check if contact is present, if yes, then update the value using contact's text field, if contact is not present check if account is present, if yes, update the value from the account's text field, else simply update the value as 'NA'