Safari > Preferences > Privacy > Website tracking
Uncheck the boxes beside > Prevent cross-site tracking
Cookies and website data:
Uncheck the box beside “Block all cookies”.
Click Safari in the menu bar then” Settings for This Website”.
Click inside the box next to Pop-up Windows” and choose “Allow”.
If the step posted doesn't help
Few users who had this problem were able to resolve the issue by running Safari Technology Preview browser.
This version of Safari has advanced features’ Download Safari Technology Preview
Safari Technology Preview > Preferences > Privacy
UnCheck the boxes beside “Prevent cross-site tracking” and “Block all cookies”.
Safari > Preferences > Websites > Pop-ups
Choose “Allow” in the box next to website’s address.
Test.