When I work with a lot of customers there is throttling 429 too many requests.
Theu issue should be the API overload
The other issue is if the customer is making the call with the different app registration across the tenant.
Lot of people ask how much quota they use across the tenant, is there any way to see the quota request across the azure portal.
|Request Type||Limit per app per tenant||Limit per tenant for all apps|
|Any||500 requests per 10 seconds||1000 requests per 10 seconds|
|Any||15000 requests per 3600 seconds||30000 requests per 3600 seconds|
|GET me/Assignment||50 requests per 10 seconds||150 requests per 10 seconds|