Thanks Karl Heinz
As you pointed out, there should be only one .ino file in the project folder.
The github repository incudes two ino files, but the project folder should only have one ino file in it.
Normally the IDE will take care of this automatically. It shouldn't be neccessary to delete or rename files manually.
But perhaps the IDE behaves slightly differently on a Mac than under Windows or Linux?
This is what I normally do under Windows:
1. on the github page, press the green button "clone or download"
2. Open the downloaded file "bitX40-master.zip" and extract all files to a location of your choice
3. Go to the extracted folder "bitX40-master" and open it
4. Inside this folder there are several files. Find the file named "raduino_v1.27.7.ino" and double click it
5. The Arduino IDE will start
6. A message box will pop-up: The file "raduino_v1.27.7.ino" needs to be in a sketch folder named "raduino_v1.27.7". Create this folder, move the file, and continue?. Click YES.
7. This will create the sketch folder with ONLY one ino file in it.
8. When you go to Sketch => Verify/Compile (or press ctrl-R), then the sketch should be compiled without errors.
When you follow exactly these steps, does this not work on a Mac?
73 Allard PE1NWL
Allard PE1NWL