Technically free, you can assign services to your clients on the back-end without them subscribing. So yes, you can create free services on ManyRequests and this can be done manually.
How can I create a Free Service on ManyRequests?
On your Dashboard, go to Users > Clients
Click the Organizations tab
Select the client you want to add a free service to
Click on the "New Service or Subscription" button
Choose the service for your client
Once done, click on the Confirm button