All vendors that you will use in Acctivate are set-up and maintained in QuickBooks. Acctivate does not have an interface to allow vendor information to be modified, this must be done in QuickBooks.
To get to the Vendor List in QuickBooks, go to Vendors > Vendor Center > Add New Vendor.
You must Synchronize with QuickBooks to copy new and updated vendors from QuickBooks into Acctivate. Once this has been done, you can create a new Purchase Order for the new vendor.