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When it comes to the plug-in installation, we actually recommend you contact your store developer or Magento Solutions Partner if you need assistance with the plug-in installation process, as the process can differ based on the unique Apache server configuration. I just don't want to make recommendations without that baseline knowledge and end up pointing us in the wrong direction.
The web setup wizard is deprecated (no longer used). The preferred installation method is composer. Composer is a command-line package management tool which allows you to install and update extensions within Magento. You will need terminal (ssh) access to your server.
The last time I installed ShipStation was version 2.2.2 which came in a zipped folder that was placed on the web server in the app/code directory. A few days ago, I checked for an update (in Magento Marketplace) and noticed the composer package name - auctane/api. To install it, you would issue this command - composer require auctane/api.
After installing the package, I noticed an error after trying to connect to my store from shipstation.com. I have an open ticket to address this issue. It seems to be a code problem with the ShipStation package. My Magento logs show this -
main.CRITICAL: TypeError: Argument 2 passed to Auctane\Api\Model\Action\Export::addXmlElement() must be of the type string, null given, called in /h
ome/public_html/vendor/auctane/api/Model/Action/Export.php on line 354 and defined in home/public
For now, I would hold off on trying to install ShipStation until this gets resolved. I'm running Magento 2.4.2p1 on Linux.