The IRS allowed employers and self-employed people to choose to defer the employer’s portion of their social security tax payments in 2020.
For those that chose to defer payment, half of that deferral will be coming due on January 3rd, 2022 and the second half will be due on January 3rd, 2023.
Payment can be made through the Electronic Federal Tax Payment system by employers and individuals. Individuals may also use Direct Pay.
Direct Pay: https://www.irs.gov/payments/direct-pay