Knowledge Base

Cannot access Plesk-hosted website on iOS or Mac devices: The operation couldn’t be completed. Protocol error

Symptoms

On iOS/MacOS devices, when accessing a website a blank page is shown or the following error is shown:
```
The operation couldn’t be completed. Protocol error
```
Nginx is configured as proxy server in Domains > example.com > Apache & nginx settings > Proxy Mode

Cause

Issue is caused by Apache bug 59311: when http2 module is enabled both for Apache and Nginx, Apache sends an incorrect header to Nginx. When Nginx used as proxy, it passes this invalid header further to browsers causing them to refuse the connection.

In order to track the impact of this behavior, the Plesk internal request with ID PPPM-12381 has been created.

Resolution

In Plesk environment configuration where http2 is enabled both for Apache and Nginx is not supported: when Nginx acts as a proxy, it only interacts with the browsers.

To work around this issue, consider one of the following options:

Click on a section to expand

Disable http2 module in Apache

Log in to Plesk GUI
Go to Tools & Settings > Apache Web Server > Disable the module http2 > Click OK to apply the changes

Modify Nginx header configuration

Connect to the server via SSH
Run the following command:

# echo “proxy_hide_header upgrade;” > /etc/nginx/conf.d/safari_fix.conf && systemctl restart nginx