Setting or Updating the record manger field was added in 12.3.0

All versions support it:  Basic to Pro.   If you don’t specify a record manger in the merge source file for a row, OAK!Merge will use the default;  which is the user name you use to log into the database with, in OAK!Merge.  The record manager names you use, must be users in the ACT database.  They can be inactive users

The text to use for a record manger name is the exact “User Name” as displayed in the TOOLS, MANAGE USERS dialog box in ACT!