I am using SNS service to send Transactional SMS. Getting the below error in CloudWatch. It says "No quota left for account". By default the quota is 1$ and I have not crossed 1$ for this month.

Even strange thing is:

I am sending SMS to around 100 contacts.I am doing this by calling AmazonSNS.publish() in a for loop 100 times for each number in a spring-boot app. Most of the requests are failing with the below error.

If I call AmazonSNS.publish() for a single mobile number after sometime, it works and SMS is getting delivered !!

I want to know,

1. Why I am getting this error even before crossing 1$?
2. how the quota for the SMS works. If it's crossing 1$ how it works after some time?
3. Is there any limit for number of SMS sent per sec or min.
4. I have asked for increasing the quota now. How much time it will take?

For Simple Email Service there is enough documentation. But for SMS (using SNS) couldn't find answers to my questions. Any help is appreciated.

   "notification": {
       "messageId": "94cxb3e9-3fa5-5b64-b04c-e4f1d7447c7a",
       "timestamp": "2020-04-21 12:27:13.342"
   },
   "delivery": {
       "destination": "+91XXXXXXXXXX",
       "smsType": "Transactional",
       "providerResponse": "No quota left for account",
       "dwellTimeMs": 44
   },
   "status": "FAILURE"
}