I had a dataset which didn't contain month or year columns (I imported monthly spss file with no date column) and created a date column like this:

*created year and month values when I imported (in a loop) like this
gen year= 2020
gen month=`i'

*Created a monthdate column
gen monthdate = ym(year, month)
format monthdate %tm

I then wanted to drop the month of January but I keep getting an error (r(198)). Does this have to do with my data type?

*drop jan 2020
drop if monthdate == 2020m1

I also tried putting 2020m1 in quotations ("2020m1") but I got error r(109).

What am I missing?