Expert Agent’s Lettings Financials run an overnight process automatically that charges all due rents. There are a number of criteria that needs to be met before the system will run the process on an individual tenancy.
The most common reason for rent not being charged automatically when it is expected to be is the Rent Next Due date not being populated. This field is populated when the rent is charged via the Mark as Let Wizard (Tenancy Setup) but can be manually populated by clicking Edit in the tenant tab on the tenancy record.
 If a rent demand has not been created when you believe it should have been please visit Why did the rent not automatically charge for this tenancy? to see if this helps.