You can specify rules for allocating revenue across an invoice period.   When no rule is set, see this article for information about how revenue is allocated: How does ScaleXP allocate the spread of revenue - and how does the system defer revenue? 

If you want to specify rules to allocate revenue using another set of rules, just select "Account Rule Recognition" using the menu at the top right of the Customer page, as shown below.  (Go to Customers tab,>>cog at top right,>>Account Rule Recognition).

You will see a screen to "Configure Account Rules"

Click "Add Account Rule".

In the next screen, select an account, then the number of months over which to spread the revenue invoiced to that account. Then choose the % revenue to be allocated in each month for each invoice.

Use the toggle "Set start to invoice issue date?" to set the start date to the issue month, if desired. If this toggle is off, the rule will be configured using the start date found in the invoice line item text, if any.

Use the box at the top right to specify the MRR percent per month.

Once you are happy with your rule, click "Create" or "Update" to save or update it.

If you need to set up a complex rule, such as splitting a single invoice line into a fixed and a time-based element, then see this article: How to set up a complex, multi-tiered revenue allocation rule. 

To set up allocations at invoice level, such as usage based allocations, see this article: How to set up usage based revenue recognition; How to allocate revenue by percent completion .