[Answered ]-Celerybeat set to crontab(day_of_month=1) sends task multiple times in a month

By default crontab will run every minute so you need to specify minutes and hours.

Change @periodic_task(run_every=crontab(day_of_month=1)) to @periodic_task(run_every=crontab(minute=0, hour=0, day_of_month=1))

This would run the task only at midnight on the first day of the month.