The reason you’re seeing that error is that the compiler isn’t able to find the .h file from the include reference you’ve given. The simplest fix is to add the location as an additional include directory. To do this:
Open the Project->Change Runtime Versions window (this is just a quick way to open the configuration properties)
Select the Build tab
Towards the bottom is a box for adding “Additional include directories”. Select the next empty line in that box and double-click. You can type in the location of the .h file here or use the three dots to select it in the file explorer.
Another option would be to use the relative file path in the include statement, but that gets a little messy.
If you’re interested, here is the list of places the compiler checks when it sees an include statement. Libraries created within Automation Studio (i.e. from the Toolbox) generally put their .h files in the Temp/Includes directory of the project. If you make your own .h file, you’ll need to tell the compiler how to find it.
