The error message is quite explicit. It couldn't find Month in your dataset.
Without a sample of your data neither can we!
Can you provide a head( )?.
Can you provide a reprex?
If you can see Month (not month) as a column my gut feeling is there may be a rogue character that doesn't display on screen but is in the name. Janitor could be your friend. But I'm speculating...
The other time I see this is when I stupidly forget to pass my data to the mutate function!