Install fails with: 500 Internal Server Error. From there I proceeded to install the Addon directly into SharePoint. Was successful in placing the app in a site. The app though, did not work. Just sat there looking pretty in the Site Contents.
Sorry if this is a duplicate but I only found one reference to this error. The circumstances were different.
Hello! The developers will work on solving the issue but it will take a while. As a workaround, please create a team site manually, install a classic version of HelpDesk on it, go to the "About" page in settings and update the product to the latest version.
Notes:
a) the parent site had to be present - would not install as a site collection root.
b) the parent had to be a modern page for the upgrade to complete.
Thank you for the update! The developers are working now on fixing the error you encountered so in future, it won't required such difficulties with the installation.