Ajax error occurred when updating joomla

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HI Guys, My name is MIKE and having a hard time trying to get this error fixed.

I have a 3websites hosted in the same server but only one is giving this issue, even though it seems to be pretty ready for the update.

the website in questions is currently on joomla 4.03, and whenever i try to update to most recent joomla, it failed with an error AJAX LOADING ERROR. see screenshots



and the console shows this error.

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Unfortunately I cant even install the fpa as it gives 403 error when tried to execute.

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I have tried to downgrade php from 8 to 7.4 but still same issue, please let me know any suggestion as i am pretty much new to this kinda of issues. thanks alot.

[shootify]

Well guys, after a further investigation, it looks like this site was infected by malicious code, as i have exact same issue as posted here viewtopic.php?t=993109

[shootify]

so i was able to get rid of the ajax error by taking the site down and find and destroy all .htaccess files, ran the update again but couldnt completed as i get this error.