Try updating line 21 to:
Since you have a column named Category in your products table as well as your categories table it can't determine which table you are trying to search.
In reality you should consider removing the Category column from your products table entirely, since you have a CategoryID column you join on it will be enough to get the category name from your categories table and it is a good idea to not store redundant data like that.
I'd also suggest in the future to make sure your column names are unique even across tables. That way you won't have to worry about ambiguous column names in your query moving forward.