By default, the Develop menu in Safari is disabled. You need to enable it first and then next you can save the Console logs. If you've already enabled the Develop menu, you can skip to the Saving the Console logs section to save the logs.
Enabling the Develop menu
Click Safari and then select Preferences...
In the window that opens, click the Advanced tab.
At the bottom of the window, select Show Develop menu in menu bar to enable the Develop menu.
Saving the HAR logs
Click Develop to open a menu.
Select Show Web Inspector.
Click the Network tab.
Reproduce the issue.
Click Export to download the logs as HAR file at a location that you specify.