What is the difference between the “Master Name” and the “Instance Name”. In some cases I only have one instance for the font.
Masters: are what you draw. Master names are arbitrary, they do not matter for the eventual exported font, only you will ever see them. You usually have very few masters.
Instances: are the font styles and variants that are being exported. The font files you have for installing in Font Book. The Style Names matter, because that is how the fonts are named in the Font Style menus (Regular, Bold, etc.). You will typically have many instances, especially if you interpolate between masters or make variants (different subsetting and post-processing).
Great! Thanks for your fast reply to that! Case closed