There are two different Query Explorers, one for Universal Analytics and one for Google Analytics 4. Both can be found here.
However, make sure you have toggled on the right view (refer to screenshot below) and are logged in to the Google account that has access to the Analytics property that you wish to troubleshoot.
In this example we will focus primarily on the Query Explorer for Google Analytics 4 but the same steps can more or less be applied to the Universal Analytics too.
The only necessary parameters that need to be filled are:
start_date and end_date
dimensions (date must always be included as we do so in Funnel's requests as well)
Please keep in mind that the dimensions must match exactly to the ones you have included in your Funnel data source when connecting. Different metric combinations very rarely lead to mismatches.
An overview of the parameters that are included in your data source can be seen under the definition label in your specific data source details. It can happen that the list of parameters is too long to be displayed in this view. In those cases you may refer to the "Edit Configuration" window.
Finally, scroll down and click on the "Make request" button. The result can be viewed as a table or a JSON and you can use that result to compare them to your Data Explorer in Funnel.
If the result doesn't match, please follow this guide on how to report a data mismatch.
The tool can also be used to troubleshoot incompatible fields. Make sure to select the right property if you are troubleshooting custom fields. Select all the fields you are interested in and click “Make request”. Instead of a table of data an error will be displayed. The error message will suggest what fields could be removed to make the request compatible.