When you are first downloading and installing Showcase IDX to your WordPress website and you see Fatal error: Uncaught Error: Undefined constant "SHOWCASEIDX_AGENT_HOST", as shown above, don't be alarmed! It is most likely caused by the version of PHP you are running on the website. Let's walk through how you can check what your PHP version is and how to rollback to another version that works.
Checking PHP Version
You are going to download and install a new plugin on your website called "Display PHP Version".
Go to Plugins, click Add New and then search for the above plugin. Click Install and then Activate.
Once the plugin is active, navigate to your dashboard and look for a widget titled "At a Glance". This widget will tell you which version of PHP you are running.
Watch this quick video tutorial below:
If you've checked your PHP version and it's running 8 or higher, you will need to roll back to a 7 version of PHP.
You can find instructions on how to do that here. The instructions will vary depending on your hosting provider, and it may be best to check your host's help resources for further assistance.
Once your PHP is downgraded, try installing the plugin again. It should work this time!