[Python] Pandas monthly rolling window

I am looking to do a 'monthly' rolling window on daily data grouped by a category. The code below does not work as is, it leads to the following error:

ValueError: <DateOffset: months=1> is a non-fixed frequency


I know that I could use '30D' offset, however this would shift the date over time.

I'm looking for the sum of a window that spans from the x-th day of a month to that same x-th day of the J-th month. E.g. with J=1: 4th of July to 4th of August, 5th of July to 5th of August, 6th of July to 6th of August etc

I've been trying to figure this out for a few days now. Any suggestions or tipps would be very appreciated. Happy New Year.

MRE:

import pandas as pd
from io import StringIO

data = StringIO(
"""\
date logret category
2014-03-25 -0.01 A
2014-04-05 -0.02 A
2014-04-15 -0.03 A
2014-04-25 0.01 B
2014-05-05 0.03 B
2014-05-15 -0.01 A
2014-05-25 0.04 B
"""
)

df = pd.read_csv(data,sep="\s+",parse_dates=True,index_col="date")

J=1

df.groupby(['category'])['logret'].rolling(pd.DateOffset(months=J),min_periods=J*20).sum()

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