GOOD NEWS.
I just checked and confirmed that I can now save the changes on the theme panel. Thanks for all your support.
I will revert back to you, if I encounter any other challenge. Shalom.

Vlad, good day.
I have contacted my host (Hostgator).
They told me that the blockage is not by the host’s firewall.
Instead, they gave me a link to an article below to share with you the developer, which can help resolve the challenge.
https://givewp.com/documentation/core/frequent-troubleshooting-issues/admin-ajax-blocked/

Thanks Vlad.
Find below the details:

Do not post credentials on the forum !

Vlad, thanks for your support.
I have ensured the requirements are met, but I still cannot save the changes in theme panel.
Everything on the System Status looks okay, but the challenge still persists.
Please can I get someone from your team to help me look at it?

• This reply was modified 6 years by Obynogeoff.