After getting AmbaSat-TTN working with the EU frequencies, I wanted to be legal and use the US frequencies. I commented out the CFG_EU868 define in lmic/config.h and replaced it with #define CFG_US915 1. This resulted in multiple undefined constants in the setup() function of src/main.ccp.
The undefine errors occur after the #elif defined(CFG_US915) section. None of the LMIC_setupChannel calls are necessary in the US as stated in the comment. Remove these and the code compiles and works. NOTE: The LMIC_selectSubBand(1) is required.