Calendar usage limits exceeded adding attendee to an event - event-handling

Question

I'm testing Google Calendar API with service account and JWT authentication server to server.
All runs fine except when I try to create an event inside a calendar I receive the error
"code": 403,
"message": "Calendar usage limits exceeded."
The problem appears only when I add an attendee to the event.
If I try to create the same event in the same calendar without any attendee, al works fine.
I receive the same error if I try to add the attendee in a second moment after event creation.
So, at this time, I cannot invite any person to any event programmatically.
For me this is a very big problem.
Can you help me?
Thanks!
EDIT:
I'm using ApiRest with ServiceAccount and JWT token.
This is a sample running fine:
POST https://www.googleapis.com/calendar/v3/calendars/{{calendarId}}/events?access_token={{access_token}}
{
"end": {
"dateTime": "2020-01-17T14:50:05Z"
},
"start": {
"dateTime": "2020-01-17T13:50:05Z"
},
"summary": "prova",
}
while this one returns error
POST https://www.googleapis.com/calendar/v3/calendars/{{calendarId}}/events?access_token={{access_token}}
{
"end": {
"dateTime": "2020-01-17T14:50:05Z"
},
"start": {
"dateTime": "2020-01-17T13:50:05Z"
},
"attendees":[{"email":"xxxxxxxxxxxxx#gmail.com"}],
"summary": "prova",
}
returns
{
"error": {
"errors": [
{
"domain": "usageLimits",
"reason": "quotaExceeded",
"message": "Calendar usage limits exceeded."
}
],
"code": 403,
"message": "Calendar usage limits exceeded."
}
}
There is no difference between POST and PUT method that implements respectively event creation and event update.
When I add any attendee, the result is always error.

Answer 1

Searching about your issue I found out it's been a well-known problem for a while and it's been reported on Issue Tracker in these threads:
Service account is unable to invite calendar groups to calendar events
Unable to set reminders via API request
Can't send notification through service account calendar