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Frequently asked questions about SMS messaging, character limits, concatenation, and delivery.

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What is the character limit for SMS text messages?

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GSM-7 Encoding (Standard Characters)

Message LengthSegmentsCharacters per Segment
1-160 characters1160
161-1600 charactersMultiple153 (7 chars for header)
Maximum: 1,600 characters (splits into ~11 segments)

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Unicode Encoding (Special Characters)

Message LengthSegmentsCharacters per Segment
1-70 characters170
71+ charactersMultiple67 (3 chars for header)
When any Unicode character appears in your message, the entire message uses UCS-2 encoding.

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What is automatic encoding?

Automatic encoding replaces Unicode characters with GSM-7 equivalents to prevent accidental segmentation from smart quotes, em dashes, etc.

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Enable Auto-Replace

  1. Navigate to Messaging > Settings > Other Settings
  2. Enable Auto-replace

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How does SMS concatenation work?

Long messages are automatically split and reassembled:
  1. Plivo splits message into segments
  2. Concatenation header added to each segment
  3. Carrier reassembles at delivery
  4. Recipient sees single message

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Billing

Each segment is billed separately. A 200-character message = 2 segments = 2x SMS cost.

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How do I send SMS via API?

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Single Message

curl -X POST "https://api.plivo.com/v1/Account/{auth_id}/Message/" \
  -u "{auth_id}:{auth_token}" \
  -H "Content-Type: application/json" \
  -d '{
    "src": "14151234567",
    "dst": "14157654321",
    "text": "Hello from Plivo!"
  }'

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Can I send bulk SMS?

Yes. Send to multiple recipients in one request: 
curl -X POST "https://api.plivo.com/v1/Account/{auth_id}/Message/" \
  -u "{auth_id}:{auth_token}" \
  -H "Content-Type: application/json" \
  -d '{
    "src": "14151234567",
    "dst": "14157654321<14158765432<14159876543",
    "text": "Bulk message to multiple recipients"
  }'
Separate destinations with < character.

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How can I receive SMS messages on my Plivo numbers?

  1. Create an application with a message_url
  2. Assign a Plivo number to the application
  3. Plivo POSTs inbound messages to your URL

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How is an incoming message delivered to my application?

StageDescription
ReceivedPlivo receives from carrier (charged)
DeliveredSuccessfully posted to your message_url
UndeliveredFailed to deliver to your URL
If message_url is not configured, messages remain in “received” status.

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Can the source number for an outbound text message be a non-Plivo number?

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US and Canada

  • Must use Plivo number as source
  • Non-Plivo numbers not permitted (telecom regulations)

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International

  • Dynamic sender IDs may be used
  • Delivery not guaranteed for non-Plivo numbers
  • Check country coverage for sender ID support

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What are Geo-Permissions and why should I use them?

Geo-Permissions control which countries can receive your SMS, protecting against fraud.

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Default Enabled Countries

  • United States
  • United Kingdom
  • India

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How Can I Manage Geo-Permissions?

  1. Navigate to Messaging > Settings > Geo Permissions
  2. Enable/disable countries as needed
  3. Set messages-per-hour fraud thresholds

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Can I configure SMS Geo Permissions for each subaccount separately?

Yes. By default, subaccounts inherit main account settings. Override for subaccount:
  1. Go to Geo Permissions
  2. Select subaccount from dropdown
  3. Customize settings
  4. Subaccount shows “Overridden” tag
Remove override:
  1. Select overridden subaccount
  2. Click Remove Override

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Why are my outbound messages failing with error code 450?

Error 450 means “destination country barred.” The destination country is not enabled in your Geo Permissions. Enable the country in Messaging > Settings > Geo Permissions.

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What is SMS Pumping and how does Plivo protect against it?

SMS pumping is fraud where attackers flood OTP fields with fake requests to premium numbers.

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Protection Features

Enabled by default for all accounts:
  • Automated traffic analysis
  • Suspicious pattern detection
  • Alerts for unusual activity

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How to Prevent SMS Pumping Attacks?

  • Enable Geo Permissions
  • Set rate limits on OTP endpoints
  • Implement CAPTCHA on forms
  • Monitor traffic patterns
  • Use Plivo’s fraud detection tools

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How to access the message content?

Message content is stored for 7 days.

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View in Console

  1. Navigate to Messaging > Logs
  2. Search by timeframe or UUID
  3. View message details
Note: Only available if data logging is enabled.

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Why should I authorize Plivo to view my SMS content?

Allow Plivo support to view content for debugging:
  • Helps identify spam filter triggers
  • Assists with delivery issues
  • Enables content policy review

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What happens to my outbound messages if I don’t have sufficient balance?

When balance is insufficient:
  1. Messages fail with error code 900
  2. API requests fail for 2 minutes with “Insufficient Credit”
  3. Queued messages continue to fail until recharged
Set up auto-recharge to prevent interruptions.

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Why were we charged for an undelivered SMS message?

Plivo charges when a message is successfully handed off to downstream carriers. Once accepted by the carrier, Plivo has no control over final delivery. Reasons for undelivered status:
  • Invalid or unreachable destination number
  • Carrier filtering
  • Device issues (phone off, full inbox)

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What are the different SMS statuses in Plivo?

StatusDescription
queuedMessage accepted, waiting to send
sentSuccessfully passed to downstream carrier (charged)
deliveredConfirmed delivery to recipient device
undeliveredCarrier could not deliver to recipient
failedInternal error before reaching carrier (not charged)

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What are the Toll-Free Surcharges?

US carriers impose surcharges on toll-free messaging:
CarrierSurcharge per Segment
Verizon$0.0025
T-MobileVaries
AT&TVaries
Surcharges appear as separate invoice line items.

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What is the Number Lookup API?

Get information about phone numbers:
  • Local and E.164 formatting
  • Carrier information
  • Caller ID name (CNAM)
See Lookup API documentation.