1. Using the Mac computer, launch Safari, then click Safari > Settings > Advanced tab > Show Develop menu in menu bar:
2. In Safari, go to Develop > Show Page Source:
This will open the lower panels on Safari:
3. Select Network tab, and refresh the page (on top, normal refresh the page or repeat the action that caused the error). You will see the network consumption graph being built bellow:
4. When the page finishes loading, choose Export on the top right corner of the lower panel, and export the HAR file.