Reload or Refresh the Page
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💠 To refresh the screen, a user is required to press the F5 function key.
💠 After opening the web browser, reload the URL.
💠 In case the QuickBooks error 504 persists, you can switch to other methods.

Note: This is a temporary error so you need to close and open it again to check the server.

Restart your device
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After reconnecting your device, you are able to repair a number of minor problems related to the Internet. In order to restart the device, you have to switch off the router, peripherals, modem, and much more connected to your computer. Later, you can connect all the networking hardware to your device and verify whether the error is showing up or not. 

Review the Proxy Settings
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Another method to get rid of QuickBooks error 504 is to check and configure the Proxy Settings on your computer. However, it can be done in windows settings only.

💠 First, you have to open the settings app on your computer.
💠 Now, head to the proxy tab on the left.
💠 Here, you need to verify and check that the Proxy settings are set correctly.

Configure the Firewall Settings
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If your firewall settings are inappropriate then it may give rise to QuickBooks error 504. This error usually occurs when you have not added any inbound or outbound roles and due to this, the firewall doesn’t help you to access the QuickBooks. In the below-listed steps, you will learn how to add exceptions after creating inbound or outbound rules in windows firewall settings.

So let’s have a look;

💠 Navigate to the Start menu and give a click on it. 
💠 In the search bar, you have to type Windows Firewall.
💠 Then, choose the Windows Firewall option once it opens.
💠 You are required to select the Advanced Settings tab.
💠 After that, hit a right-click on the Inbound Rules option.
💠 Now, tap on the New Rule icon.
💠 Press the Next button and then hover over the Programs section.
💠 The next step is to select This Program Path.
💠 Furthermore, you need to locate the location of the QuickBooks file.
💠 When all set, hit the Next tab.
💠 Later, you have to choose the option Allow the Connection.
💠 Click the Next tab once again.
💠 Ensure that all the options are selected and verified.
💠 Now, move your cursor to the Next button and write the rule name.
💠 Finally, press the Finish tab.

When you are done with adding the inbound rule, you are supposed to follow the same steps for adding the outbound rule. All you have to do is select the Outbound Rules option in the Advanced Settings. 

Check the DNS Settings
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You may have to face difficulty while browsing QuickBooks if you recently changed your host servers or shifted your website to some other IP address. Hence, it is necessary to check and verify the DNS Settings and configure them if required. 

💠 To begin with open the Control Panel in your system.
💠 Go to the Network and Internet section.
💠 Now, you need to choose the Network and Sharing centre option.
💠 Once you are done with that, press the Change Adapter Settings button.
💠 A user is required to select the connection and then configure the DNS for it. For example;
1. If you want to adjust the Ethernet Connection, make a right-click on the Ethernet Interface and select the Properties tab.
2. In case you are using a wireless connection then hit a right-click on the Wi-Fi interface and choose the Properties option.
💠 Afterward, you have to hit the Networking tab.
💠 Under the section, This Connection uses the following items, you would have to click on the
💠 Internet Protocol Version 4 (TCP/IPv4), or you may also select the Internet Protocol Version 6 (TCP/IPv6). 
💠 Then, head to the Properties option.
💠 Next, navigate to the Advanced tab.
💠 You are required to choose the DNS tab.
💠 If you get any other IP address then note it down for further reference.
💠 Once noted, delete it from here.
💠 Later, press the OK button.
💠 The last step is to select the option: Use the following DNS server address. 
💠 When you find any other IP address in the Alternate DNS server or Preferred DNS server, you are required to write it down in case you need it in the future. 
💠 Here, you can replace these addresses with Google DNS servers Ip addresses;
1. IPv6: 2001:4860:4860::8888 and/or 2001:4860:4860::8844.
2. IPv4: 8.8.8.8 and/or 8.8.4.4.
3. IPv6-only: Instead of using IPv6 addresses, you can use Google Public DNS64.

After performing the above steps, you can test the setup whether it is working fine or not. You can also repeat the same steps if you wish to change DNS for other network connections.