Following the below-given steps to fix windows firewall is blocking QuickBooks issue.

Click on the Windows icon and select, Control Panel.
Go to the Windows Firewall window and locate where it says: “Windows firewall with adv. s.”
Then, choose New Rule and click on Program.
After that, mark the This program Path checkbox.
Browse and choose the components for the service that you want to allow. You can do this by simultaneously pressing the Ctrl + F option.
Go to the next window and choose the Allow the connection option. Then, click Next.
Further, make sure to mark every checkbox that appears on your screen.
At last, you have to enter the name of the rule. For example: Payroll Allow.
Follow the same steps for allowing the outbound connection. For this, select the outbound option and then click on create a rule. After that, open the QuickBooks Desktop application. If the Windows firewall is blocking QuickBooks issue persists even then, try to turn off the Windows firewall.