how to add solo 401k employee and employer contribution on payroll?

You've come to the right place for assistance, @pat107. I'll help you record employee and employer contributions to a solo 401(k) in QuickBooks Online (QBO).

To add the contribution to each of your employees, you need to run a one-time paycheck. This way, the 401(k) item will affect the employee's W-2 and payroll reports. Please note that the deadline for filing W-2 electronically in QBO is January 30. However, it's best to finish this task before year-end to avoid complications before tax filing.

Here's how to set up 401(k) contribution to each of your employees:

1. Click Payroll from the left menu, then select Employees.
2. Select each employee on the list.
3. Click Start or Edit in the Deductions & Contributions section.
4. Click + Add deduction/contribution.
5. Select Retirement Plans for the Deduction/contribution type and 401(k) for the Type.
6. Enter other necessary details, including the Employee deduction and Company contribution.
7. Click Save.
8. Repeat steps 2 to 7 for the rest of your employees.

Once done, create a one-time paycheck for your employees. 

Additionally, run payroll reports in QBO to have the necessary details about your employees' deductions and contributions, which will streamline your tax filing.

Please don't hesitate to reach out to us anytime whenever you need additional guidance setting up 401(k) contributions in QBO. I'll be happy to assist you further. Take care, and have a prosperous new year!