The steps below need to be performed to set up US Payroll in APM

Introduction

Setup of Payroll Accumulators, Entry Codes, and Rates is required for the calculation of US Payroll Taxes and Contributions.

1. Define Accumulators for Taxes and Contributions basis

Payroll > Entry codes Accumulators: define Accumulators for calculation of Federal Income Tax (ACC 25) and other taxes and contributions:

Define Entry codes that should be a part of Basis for Federal Income Tax and other Taxes and Contributions:

If you pay Supplemental Wages with Regular Wages and need to withhold Federal Income Tax as if the total were a single payment for a regular payroll period, then set up the Supplemental Wages ECs the same way as shown above - add to ACC25.
If you need to withhold Federal Income Tax on the Supplemental Wages at a flat Tax Rate, then set up the Supplemental Wage ECs to save amounts into a separate accumulator - ACC43, and modify the script with the line W92=W92+L61:

Payroll > General:

Set option Payroll Enabled, define current Payroll period

Define National Payroll Code=US United States

Select Accumulator for US Federal Taxable Wages

Set option Limit reports and documents settings by National Code:

Top organization unit > Rates: define Global Rates used for calculation of US taxes and contributions:

Payroll > Entry Codes: add System Entry codes 930 and 931 which will be used for calculation of Federal Income Tax:

Add other Tax and contribution Entry codes:

Social Security Tax

Medicare Tax

FUTA Tax

SUTA Tax

401 (K) Pre-Tax

401 (K) Post-Tax

401 (K) Catch Up

401 (K) Roth contribution

Medical Co-Pay

Union Contributions (AMO Pension Plan, SIU Vacation Plan etc)

Please check this article for details.