Error connecting to Connector in Joomla 5

[bullgator2k]

Hoping for some insight due to the obscure nature of the issue (site setup is unable to provide details without debug).
Apologies in advance if I have not provided enough info.

The site is on Joomla 5.
Created cache bypass rule for api uri in Cloudflare.
Bypassed Cloudflare caching for entire site.
Temporarily disabled MFA and regenerated my API key, but there was no change in outcome.

Turned on debug in Global Config and believe I captured a relevant event in logs/everything.php that occurred immediately upon clicking save:

2025-02-09T19:58:24+00:00 INFO 74.208.58.182 tokenfailure Authentication failed
2025-02-09T19:58:24+00:00 CRITICAL 74.208.58.182 error Uncaught Throwable of type Joomla\CMS\Access\Exception\AuthenticationFailed thrown with message "". Stack trace: #0 [ROOT]/libraries/src/Application/ApiApplication.php(110): Joomla\CMS\Application\ApiApplication->route()
#1 [ROOT]/libraries/src/Application/CMSApplication.php(306): Joomla\CMS\Application\ApiApplication->doExecute()
#2 [ROOT]/api/includes/app.php(50): Joomla\CMS\Application\CMSApplication->execute()
#3 [ROOT]/api/index.php(31): require_once('/homepages/8/d3...')
#4 {main}
2025-02-09T19:58:24+00:00 CRITICAL 74.208.58.182 error Uncaught Throwable of type InvalidArgumentException thrown with message "Error loading menu: api". Stack trace: #0 [ROOT]/libraries/src/Application/CMSApplication.php(592): Joomla\CMS\Menu\MenuFactory->createMenu()
#1 [ROOT]/plugins/system/inlinecontent/inlinecontent.php(236): Joomla\CMS\Application\CMSApplication->getMenu()
#2 [ROOT]/libraries/src/Plugin/CMSPlugin.php(289): PlgSystemInlineContent->onAfterDispatch()
#3 [ROOT]/libraries/vendor/joomla/event/src/Dispatcher.php(454): Joomla\CMS\Plugin\CMSPlugin->Joomla\CMS\Plugin{closure}()
#4 [ROOT]/libraries/vendor/joomla/application/src/AbstractApplication.php(99): Joomla\Event\Dispatcher->dispatch()
#5 [ROOT]/libraries/src/Application/ApiApplication.php(437): Joomla\Application\AbstractApplication->dispatchEvent()
#6 [ROOT]/libraries/src/Application/ApiApplication.php(116): Joomla\CMS\Application\ApiApplication->dispatch()
#7 [ROOT]/libraries/src/Application/CMSApplication.php(306): Joomla\CMS\Application\ApiApplication->doExecute()
#8 [ROOT]/api/includes/app.php(50): Joomla\CMS\Application\CMSApplication->execute()
#9 [ROOT]/api/index.php(31): require_once('/homepages/8/d3...')
#10 {main}

Result from enabling debug in Panopticon System Config when trying to save site:

HTTP Status 500

HTTP Body
{"errors":[{"code":500,"title":"Internal server error"}]}

HTTP HEADERS
Date
Sun, 09 Feb 2025 19:31:38 GMT

Content-Type
application/vnd.api+json; charset=utf-8

Transfer-Encoding
chunked

Connection
keep-alive

x-frame-options
SAMEORIGIN

referrer-policy
strict-origin-when-cross-origin

cross-origin-opener-policy
same-origin

X-Powered-By
JoomlaAPI/1.0

Expires
Wed, 17 Aug 2005 00:00:00 GMT

Cache-Control
no-store, no-cache, must-revalidate, post-check=0, pre-check=0

Pragma
no-cache

Last-Modified
Sun, 09 Feb 2025 19:31:38 GMT

cf-cache-status
DYNAMIC

Report-To
{"endpoints":[{"url":"https://a.nel.cloudflare.com/report/v4?s=uHx3oEayvKKQen6M8NiBI53qybsUuD%2FhjADgict%2Fw5Prr3o8kqaP0AngJ%2BiQWVmse1eiLEne87ooFwc%2BuKb67kWmsMMXV9Von6tAo8%2Flb2ONADohckrmt6YskPT8vS3Ai3LDMliqJ1iM"}],"group":"cf-nel","max_age":604800}

NEL
{"success_fraction":0,"report_to":"cf-nel","max_age":604800}

Server
cloudflare

CF-RAY
90f647e0b9aed19e-MCI

server-timing
cfL4;desc="?proto=TCP&rtt=1107&min_rtt=671&rtt_var=952&sent=8&recv=9&lost=0&retrans=0&sent_bytes=4571&recv_bytes=1182&delivery_rate=3751295&cwnd=254&unsent_bytes=0&cid=0049707ef7baf3ed&ts=600&x=0"

[nikosdion]

As per the backtrace, the problem is the third party plugin Plg_System_InlineContent.

Side note: this is literally the first troubleshooting step I have documented. Please read it, and do contact the plugin's developer. The mistake they are doing is that they are trying to access the Joomla menu which WILL NOT work on the Api or CLI application, thus breaking Joomla. The blog post I have linked to will tell them what they need to do.