After setting phone_number via Auth.updateUserAttributes(), no verification code (SMS) is sent

Please note that the Monthly Spending Limit is a limit set by AWS that you cannot exceed unless a limit increase support case [1] is created. You must increase your account’s SNS SMS monthly spending limit [1] for sending SMS messages in Amazon SNS.

Additionally, I would like to mention that you may also create an SMS spending alarm [2] [3] using CloudWatch. It can notify you when your SMS spending exceeds a certain amount (threshold). This can help you in taking timely actions without halting the SMS capabilities of your account. You can set up CloudWatch to deliver these notifications to you by SMS, Email etc. via SNS topic.

You can monitor the spending as well [4]

Also, if quota is not an issue, you can enable cloudwatch logs[5] to see the failure and success logs

References: [1] https://aws.amazon.com/premiumsupport/knowledge-center/sns-sms-spending-limit-increase/ [2] https://docs.aws.amazon.com/pinpoint/latest/userguide/channels-sms-monitor-spending.html#channels-sms-monitor-spending-alarms [3]https://aws.amazon.com/premiumsupport/knowledge-center/sns-sms-spending-limit-alarm/ [4]https://docs.aws.amazon.com/sms-voice/latest/userguide/monitor-spending.html [5]https://docs.aws.amazon.com/sns/latest/dg/sms_stats_cloudwatch.html

Adding to the previous answer, you can get your limit increased in sandbox mode as well