It is not necessary to purchase an additional license to process transactions for more than one company.
If you are processing payroll for three companies, and each has one bank account, you would create three separate Accounts within ACH Universal. There is a one-to-one relationship between each bank account and the ACH Universal Account. (If one of those companies was processing ACH transactions using two different bank accounts, for instance, you would need four separate Accounts within ACH Universal.)
The Standard/Desktop edition of ACH Universal, by default, comes with 20 available Accounts. If you have a subscription license, as a supported customer, you may request as many Accounts as you need. If you have a traditional license, requesting additional Accounts would be considered an upgrade.
*If you are a third-party processor (e.g., CPA firms and payroll processors), and you are processing ACH transmission files on behalf of many companies, you should have a Processor-level license for multiple- origination transmission files.