Be sure that all of your files are in .wav format 24bit at 44100Hz.
For Stereo Mastering and Stem Mastering: is really important that your pre-master audio file do NOT exceed -6dB of peaks. The reason is to have enough “headroom” for the mastering process.
For Stem Mastering: be sure that your stems are in this order KICK, PERCUSSIONS, BASS, SYNTHS, GUITARS, PADS, VOCALS, FX.
For Mixing Service: please name all tracks before you send me the files.