Errors after upgrade to Joomla 4

Hello.

I just performed an upgrade of Joomla from Joomla 3 to Joomla 4, and now get errors during the System Check. This is after testing the upgrade in a staging area and not getting these errors.

At first I saw the error:
Invalid response value detected

I then turned on debugging in Moodle and now see this:
Invalid response value detected test_data => Invalid response value detected: Scalar type expected, array or object received.

The file /logs/joomdle_system_check.json shows:
{"exception":"invalid_response_exception","errorcode":"invalidresponse","message":"Invalid response value detected","debuginfo":"test_data => Invalid response value detected: Scalar type expected, array or object received."}

The file /moodledata/temp/joomdle_system_check.json shows:
{"error":true,"code":404,"message":"Page not found","trace":"#0 \/home\/wcep\/public_html\/libraries\/src\/Application\/SiteApplication.php(746): Joomla\\CMS\\Router\\Router->parse()\n#1 \/home\/wcep\/public_html\/libraries\/src\/Application\/SiteApplication.php(232): Joomla\\CMS\\Application\\SiteApplication->route()\n#2 \/home\/wcep\/public_html\/libraries\/src\/Application\/CMSApplication.php(293): Joomla\\CMS\\Application\\SiteApplication->doExecute()\n#3 \/home\/wcep\/public_html\/includes\/app.php(61): Joomla\\CMS\\Application\\CMSApplication->execute()\n#4 \/home\/wcep\/public_html\/index.php(32): require_once('\/home\/wcep\/publ...')\n#5 {main}"}

I am stuck and not sure what to make of this. Does anyone have any thoughts on what is wrong? Any help would be appreciated as the site is not functioning properly at the moment.

Thank you.

It seems the problem is with Joomla...as you are getting Joomla errors in the raw reply in Moodle:
error":true,"code":404,"message":"Page not found

If you can't find the issue, you can email me and I'll take a quick look.

I have emailed you the access information for the website. I am stuck.
Thanks for the help.

This issue has been solved and it was embarrassingly simple. In Moodle, in the Joomdle configuration there, in the Joomla URL, there was a trailing slash after the URL. That caused the web services to not connect properly.

Removed that slash and it now works perfectly.

Thank you Antonio for your help with this!