According to this webpage,
reportType: SUBSCRIPTION_EVENT only supports frecuency DAILY at version 1_3 ; doesn't support fecuency MONTHLY.
But you can get more days if you use the filter[reportDate] parameter and, by code, iterate over a date range.
https://api.appstoreconnect.apple.com/v1/salesReports?filter\[reportDate\]=2021-11-01&filter[frequency]=DAILY&filter[reportSubType]=SUMMARY&filter[reportType]=SUBSCRIPTION_EVENT&filter[vendorNumber]=*****&filter[version]=1_3
Topic:
App Store Distribution & Marketing
SubTopic:
App Store Connect API
Tags: