On top of what was already replied,
There are multiple ways of accessing the GP data from the SQL back-end without having to resort to complex API or Gateway setups (which often come with multiple security and system settings to put in place).
If your goal is simply to consume the data for end-users directly in Excel, SSRS, Crystal Report or PowerBI, there are about 200 out-of-the-box pre-built SQL views that Microsoft provides for free and that are already installed in GP.
You can start with the GP Reporting Setup where you can deploy built-in SSRS & Excel reports that cover all the modules in GP. They more or less mimic the content of the built-in SmartLists from GP.
Excel is my favorite on that side, as it's deployed in no time, doesn't require much setup and security can be tackled very quickly too. Today's PowerQuery language in Excel & PowerBI allow you to create some nice dashboards.
BTW, Microsoft already provides a few of those DashBoards when you deploy the Excel reports..
Have a look at them
PM me if you need any help on that side.
B@
aka GP Geek