How to build it?

Pull the repo with recursive submodule initialization and then run ./build.ps1 command to build the app. Once done archives with all the necessary .FAP and .FAL files will be available in the build directory.

Just in case if you would like to build not via ./build.ps1 file then you have to revise totp/features_config.h file and ensure that this line #define TOTP_TARGET_FIRMWARE TOTP_FIRMWARE_XTREME_UL targets your firmware. If it is not, then you have to update this line by changing it to #define TOTP_TARGET_FIRMWARE TOTP_FIRMWARE_OFFICIAL_STABLE or #define TOTP_TARGET_FIRMWARE TOTP_FIRMWARE_OFFICIAL_DEV, depends on target firmware you are building app for.