[Solved: Unauthorized WOPI host.]: Failed to establish socket connection or socket connection closed unexpectedly.

Question: How do you solve Next Cloud-All-in-One error that says 
"Failed to establish socket connection or socket connection closed unexpectedly. The reverse proxy might be misconfigured, please contact the administrator. For more info on proxy configuration please checkout https://sdk.collaboraonline.com/docs/installation/Proxy_settings.html"

Or sometimes it says "Unauthorized WOPI host. Please try again later and report to your administrator if the issue persists".

Or Next Cloud cannot empty the IP Whitlist box


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Answer: There is a chance that you are not clicking the arrow next to the IP-Whitlist text box. I spent hours looking for information but could not find it.

If you need to update WOPI IP Address, you need to edit the textbox then click on the --> next to the text box in order to save the changes in the IP Whitlist textbox.