If you have some employees that are paid bi-weekly, and some that are monthly, here's how to make that happen.
Go to Employees > Manage Accruals (prior to April 2021, this was labeled Manage Allocation).
Now click Add New, and you will be able to give your Accrual a title, choose the employees that will use that Accrual type, and enter the spread that you require.
There's no need to calculate percentages or do any math, for example in the screen shot below, we have a Bi-weekly spread, so we entered the pay periods as they land in each month, and we have a Working Days Accrual, so we just entered the number of working days in each month.
When you are working in the Manage Payroll screen for each employee, you will be able to choose/change the accrual type there as well.