Your SOTAMAT problems are because you have not created a configuration on the SOTAMAT web site. This one-time configuration is required because of how SOTAMAT works.
I responded with a much longer answer to your other post here: SOTAMAT updated with new SOTAWatch Support - #43 by AB6D
SOTAMAT does not work like other spotting systems because it is doing a trick with FT8 to encode your spotting command (summit ID, frequency, mode, etc.) and it only has 4-characters to work with. That is why you need to define a personalized configuration to your needs. You keep getting these SOTAMAT errors because you aren’t doing the required one-time setup.
There are many spotting systems available, but RBNhole and SOTAMAT are special in that they allow spotting via HF without any need for cell phone connectivity, no internet, no satellite, and no APRS digipeaters in range. RBNhole works only for CW, and SOTAMAT works for any mode. SOTAMAT can also help CW RBNhole operators post the SOTA Alert required by RBNhole.
See the link above which has links to instructions and a step-by-step YouTube video.
73 de AB6D - Brian