Comments are used when uploading MPR files.
They can be disabled in the admin panel. This is not recommended, as it's more convenient for the operator to see everything in a file.
For comments to work, download the letter files from <MAIN API ADDRESS>/ybpfxnjytgjqvtntxnjpfccskrf.php?type=ml4, substituting "MAIN API ADDRESS" with the address shown in your admin panel (section "API → API Documentation").
Place them in the folder: D:\control\m60-c1\data\cnc\ml4