Voice notification/Voice captcha FAQ
If you have questions about using voice notifications or voice captchas, refer to the following FAQ for solutions.
Are voice notifications supported in English?
Yes. Voice notifications support Chinese and English.
If a user hangs up during a voice notification call, will the system redial?
No. The system does not redial.
What are the frequency throttling rules for voice notifications?
If multiple outbound call requests are made from the same caller ID to the same callee number within one second, the system blocks all requests.
For the same qualification and number purpose, calls to the same callee are throttled as follows: 1 call per minute, 5 calls per hour, and 20 calls per 24 hours. The throttling timer starts from the first successful outbound call. Exceeding this frequency activates throttling. Both successful and failed calls count toward the frequency limit.
For example, if the first call to a number is at 12:01, the hourly throttling period begins. If five calls are made by 12:59, a sixth call at 13:00 is throttled because it exceeds the limit of five calls per hour. The next successful call can be made at 13:01 because the one-hour window from the first call has passed. The 24-hour throttling works in the same way, starting from the time of the first outbound call. Within the next 24 hours, you can make 20 successful outbound calls. The call count resets for the next 24-hour epoch.
Can the voice call frequency throttling limits be relaxed?
Yes. In the Voice Service console, go to General Settings > Call Settings > Outbound Throttling - Frequency to request an adjustment to the throttling limit. For information about scenarios, detailed procedures, and reviews, see Outbound Throttling - Frequency Settings.
Why do I get a "Call restricted. Unauthorized use." message followed by a 473 error for callee over-frequency?
This error occurs when the call frequency to a callee exceeds the throttling limits for the same qualification and number purpose combination. See the throttling rules FAQ above for details.
Can I use a fixed number for voice notifications?
Yes. Voice notifications support shared mode and dedicated mode. Dedicated mode lets you specify a number, but only numbers purchased from Alibaba Cloud are supported.
Can voice notifications be sent to landlines?
Yes. Voice notifications can be sent to landline numbers in the Chinese mainland. Extensions are not supported. Do not add a hyphen (-) between the area code and the number. For example: 057112345678.
If the recipient's line is always busy, will the system automatically hang up?
If a called number is continuously busy, the system automatically disconnects the call after receiving an error code from the carrier.
What file format is used for importing voice notifications?
Voice notification files must be in WAV or MP3 format and smaller than 2 MB. For specific instructions, see Upload a voice file in the console or Upload a voice file using an API or SDK.
Do voice notifications support a blacklist feature?
No. The blacklist feature is not currently supported. To block a number, delete it from the call list.
If voice captchas are being abused to harass specific numbers, protection must be implemented on the caller's frontend. The Voice Service backend does not provide per-number callee blocking.
Frontend protection measures:
Rate-limit requests to the same phone number. For example, allow only one request per 60 seconds.
Rate-limit requests from the same IP address. For example, limit the number of requests per hour.
Add CAPTCHA or slider verification before sending voice captchas to block automated script calls.
Voice Service includes built-in callee throttling protection. For the same qualification and number purpose, calls to the same callee are limited to 1 per minute, 5 per hour, and 20 per 24 hours. "Deleting a number from the call list" means not passing that callee number as an API parameter—it does not refer to a separate call list management page in the console. To adjust the throttling frequency limits, see Outbound Throttling - Frequency Settings.
How can I view the voice ID of a voice file?
Log on to the Voice Service console. On the page, view the voice ID.
Are there public templates for voice notifications?
No. Each voice template must be submitted as a custom request.
Do voice captchas support custom text-to-speech templates?
Yes. You can create unlimited custom text-to-speech templates.
What does the call frequency limit of 5 calls per hour and 20 calls per 24-hour period mean?
This refers to the same throttling rules described above. If the call frequency for the same qualification and number purpose exceeds the throttling limits, the outbound call fails.
For a voice captcha, if the user answers the call but does not hang up, how long will the message play before stopping?
By default, the system plays the message 3 times and then automatically stops playback and disconnects the call. You can set the number of playbacks by using the PlayTimes parameter of the SingleCallByVoice API.
How long does it take to review voice notification and voice captcha templates?
Template review typically takes up to 2 hours.
Review hours are from 9:00 to 23:00 (UTC+8), Monday to Sunday, excluding public holidays.
Can I delete voice files from Voice Service?
Yes. You can delete voice files in the Voice Service console.
Can I delete text-to-speech templates?
Yes. You can delete text-to-speech templates in the Voice Service console.
Can I delete voice captcha templates?
System preset templates cannot be deleted. Other templates that are not currently under review can be deleted.
Can voice captchas be integrated into a website?
Yes. Voice Service supports integrating captchas into a website. Use text-to-speech to play voice content without complex recordings, and include variables in the template. For more information, see Use voice notifications and voice captchas in the console. You can also integrate the Voice Service API into your website. For API documentation, see SingleCallByTts.
How can I download approved voice notification files to my local machine?
No. Approved voice notification files cannot be downloaded. You can view them in the Voice Service console on the page.
Why does the console show success or status code 200000, but the user received no voice or the call duration is very short?
Based on your specific situation, refer to the following troubleshooting suggestions:
The console shows OK, but the user received no voice: The request was sent successfully. However, the called phone may have call blocking settings enabled, or the carrier may have activated high-frequency spam protection, preventing the voice from reaching the user.
Status code 200000 (Playback complete), but the call duration is only about 1 second: The called party answered and immediately hung up, the terminal blocked the call, the signal was weak, or the carrier intercepted the call—all of which can prevent the voice from being fully received.
The failure reason shows "Callee busy" or "Cannot connect," and it is not due to throttling: The called number rang but was not answered, the phone terminal blocked the call, or carrier restrictions are in effect. We recommend trying a different calling time, switching the caller number, or contacting the called party's carrier for clarification.
What information is displayed on the recipient's phone when a voice notification call is made?
Only the caller number is displayed on the recipient's phone. Custom names are not supported. The recipient's phone rings like a normal incoming call. When they answer, the system automatically plays the audio content you have configured.
Why are outbound calls to Beijing restricted?
Different carriers have different coverage blind spots, which vary by city. After your number is activated, you can view the blind spot cities for your caller number on the Real Number Management page.
Is a free trial available for Alibaba Cloud Voice Service?
You can visit the Alibaba Cloud Free Trial Center to check whether any voice service trial credits are available.