I was finally able to see the error in my Browser Console.
Browser Console
Network tab
(Larger view of Network tab here: https://forum.osticket.com/assets/files/2022-09-25/1664145067-205421-network-log.png)
Headers (under the Network tab):
Request URL: https://[redacted].com/support/open.php
Request Method: POST
Status Code: 404
Remote Address: [redacted]:443
Referrer Policy: no-referrer-when-downgrade
alt-svc: h3=":443"; ma=86400, h3-29=":443"; ma=86400
cache-control: no-cache, must-revalidate, max-age=0
cf-cache-status: DYNAMIC
cf-ray: 7507ad435b97335a-EWR
content-encoding: br
content-type: text/html; charset=UTF-8
date: Sun, 25 Sep 2022 23:53:11 GMT
expires: Wed, 11 Jan 1984 05:00:00 GMT
link: <https://[redacted].com/wp-json/>; rel="https://api.w.org/"
nel: {"success_fraction":0,"report_to":"cf-nel","max_age":604800}
referrer-policy: no-referrer-when-downgrade
report-to: {"endpoints":[{"url":"https:\/\/a.nel.cloudflare.com\/report\/v3?s=zFkYMbaB%2BsikdJ8mv6hpe3Fh8ELvGk7fRDNm%2BKIMpJ0woU3hD8rylN7IdPQ312H1q9kiWmXsdEJnPl9QspdtV%2BSkRlgf64AXISEe6NBgtt9%2BHa6jsrIZzNJPVbP4jFZgTp0b0yTKoQI%3D"}],"group":"cf-nel","max_age":604800}
server: cloudflare
vary: X-Forwarded-Proto,Accept-Encoding,User-Agent
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
:authority: [redacted].com
:method: POST
:path: /support/open.php
:scheme: https
accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,/;q=0.8,application/signed-exchange;v=b3;q=0.9
accept-encoding: gzip, deflate, br
accept-language: en-US,en;q=0.9
cache-control: max-age=0
content-length: 1088
content-type: multipart/form-data; boundary=----WebKitFormBoundaryefwbJCYH5i3Ldoxn
cookie: OSTSESSID=3125e21a58d83124a4180ece7245a120; wp-settings-1=libraryContent%3Dbrowse%26edit_element_vcUIPanelWidth%3D1073%26edit_element_vcUIPanelLeft%3D337px%26edit_element_vcUIPanelTop%3D0px%26editor%3Dhtml%26post_settings_vcUIPanelWidth%3D650%26post_settings_vcUIPanelLeft%3D542px%26post_settings_vcUIPanelTop%3D175px%26advImgDetails%3Dshow%26imgsize%3Dfull%26mfold%3Do%26panel_vcUIPanelWidth%3D650%26panel_vcUIPanelLeft%3D463px%26panel_vcUIPanelTop%3D74px; wp-settings-time-1=1636075679; wpda_search_information_schema_tables=malware; wpda_schema_name=i3670938_wp1; wordpress_logged_in_82e855fb87b6d4e76a2f863ef7e88cbd=1547portal%7C1664154062%7Ct3ZDoHwiAnMoKqHmkBvSQm4UK9G9oXhIHpcMNngiz61%7Ce53eaa44491852abdb937c4fd1f0db9dd887d71f9e10d89ac946e14fdbb94ed9; PHPSESSID=fd9e805c72e640ebee21fa66989eeb1c
origin: https://[redacted].com
referer: https://[redacted].com/support/open.php
sec-ch-ua: "Google Chrome";v="105", "Not)A;Brand";v="8", "Chromium";v="105"
sec-ch-ua-mobile: ?0
sec-ch-ua-platform: "Windows"
sec-fetch-dest: document
sec-fetch-mode: navigate
sec-fetch-site: same-origin
sec-fetch-user: ?1
upgrade-insecure-requests: 1
user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/105.0.0.0 Safari/537.36
Sources tab
Shows "no resource with given URL found" for open.php.
"No resource with given URL found" appears on the Sources tab when using PHP v 7.4.3, though it only causes the 404 error page and failure to create the ticket in PHP v 8.0. Yet open.php is there in the folder where it should be.