Updating the model, there are no output symbols

Hi,

in my everyday work-routine I have some repetitive tasks, which I need go through many times. So I would like to automate it with some speech commands.

I found this model (models/vosk-model-small-en-us-zamia-0.5(49M)) suitable for my purpose, but I wanted to improve the recognition of my specific commands(words). So I followed this steps: https://alphacephei.com/vosk/adaptation , the "Updating the language model" section. But while building the grammar I ended up with this error: "... fstsymbols: Saving osymbols but there are no output symbols".
My text.txt contains only these 3 lines for example(these aren't new words for this model):
resistor
mega
kilo

Is it possible to make modification on this model like this? (I was able to build the grammar on another model: vosk-model-en-us-0.22-lgraph(128M), but this model doesn't works well for me).
Thank you for any advice.