How to fix WHMCS error Call to undefined method WHMCS\Http\Client\HttpClient

WHMCS Error:

Error: Call to undefined method WHMCS\Http\Client\HttpClient::requestAsync() in

Rename vendor/ and modules/ folders

[email protected] [/home/user/public_html/hosting]# mv vendor/ vendor_old
[email protected] [/home/user/public_html/hosting]# mv modules/ modules_old

Upload fresh appropriate WHMCS version files into temp folder, for example: whmcstemp/

Copy vendor/ and modules/ folders from whmcstemp into your WHMCS installation folder:

[email protected] [/home/user/public_html/hosting]# cp -rp ../whmcstemp/vendor/
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cPanel, WHMCS xml-api 404 error

Server's logs where you can see 404 not found error

"GET /xml-api/suspendacct?user=hiden&reason=test HTTP/1.1" 404 0 "-" "-" "a" "-" 2087
"GET /xml-api/suspendacct?user=hiden&reason=test HTTP/1.1" 404 0 "-" "-" "a" "-" 2087
"GET /xml-api/suspendacct?user=hiden&reason=test HTTP/1.1" 404 0 "-" "-" "a" "-" 2087

The cause of this usually outdated WHMCS version

Support for the XML-like output of our API was removed from the product in cPanel & WHM version 74:

Removed XML output in API functions
In cPanel & WHM version 74, we removed the Extensible Markup Language (XML) output format from all of our API functions.… Read the rest