Twilio error 63015 is thrown when your application attempts to send a freeform (non-template) WhatsApp message to a recipient, but the 24-hour customer service window that was opened by the recipient's last inbound message has expired. WhatsApp's Business Messaging Policy requires that all business-initiated messaging outside the 24-hour window use pre-approved message templates, and attempting to send any freeform content after the window closes generates this error. The 24-hour window resets every time the recipient sends any inbound message to your business number, giving you a fresh 24-hour period for freeform replies.
What Causes This Error
A recipient who sent your business a message more than 24 hours ago and has not sent any subsequent message has caused the session window to expire, meaning any freeform reply your application sends after that 24-hour mark violates WhatsApp's session messaging rules. Delayed message processing in your application, where an inbound message is queued and your response is generated and sent after processing delays push the response time past the 24-hour window, is a common operational cause that is especially problematic for low-volume or batch-processed conversation workflows. Manual review processes where a human agent takes more than 24 hours to compose and send a reply to a customer inquiry will consistently hit 63015 for any conversation that falls outside the window before the agent responds. Applications that track conversation state incorrectly, for example using the time of the last outbound message rather than the time of the last inbound message to calculate window expiry, will miscalculate session availability and attempt freeform sends when the window has already closed.
How to Fix It Step by Step
Update your message handling code to check whether the 24-hour session window is still open before sending a freeform message: retrieve the timestamp of the most recent inbound message from the conversation participant (stored in your application's conversation log or queryable from the Twilio Conversations API) and compare it to the current UTC time, switching to template-based sending if the window has expired. When 63015 is encountered in your error handler, do not retry the freeform message: instead, select an appropriate pre-approved WhatsApp template from your approved template library that serves the same conversational purpose (for example, a conversation re-engagement template or a follow-up prompt template) and send it using the ContentSid of the approved template. In the Twilio Console, navigate to Messaging, then Content Template Builder to review your approved template library and identify which templates are suitable for re-engaging a conversation that has gone past the 24-hour window: common options include a template asking the customer to confirm they still need assistance or a template providing the information the customer originally requested in a structured format. Notify human agents in your customer service platform when a conversation is approaching the 24-hour window (for example, at 22 hours) so they can either respond before the window closes or proactively send an approved template to acknowledge the customer's inquiry before the window expires.
How to Prevent It from Recurring
Implement a session window tracker in your conversation management layer that records the timestamp of every inbound message per conversation and calculates the remaining window time in real time, exposing this as a field in your agent dashboard so agents can see at a glance how much time remains before they must switch to template-based communication. Set up automated notifications at the 20-hour and 23-hour marks for any open conversation that has not received an outbound response, escalating to a supervisor if the conversation reaches the 24-hour threshold without a reply so that the customer experience is not degraded by a silent window expiry. Design your application's message routing logic to treat freeform and template sends as two distinct code paths: freeform sends always check window availability first and fall back to a template path automatically if the window is closed, never returning an error to the business logic layer that called the send function. Develop and get approval for a library of re-engagement templates that cover your most common late-response scenarios, so when the window closes you have appropriate templates ready to use rather than needing to create and submit new templates reactively.
When to Call a Specialist
If your application handles high conversation volume and you are seeing widespread 63015 errors because your processing pipeline introduces delays that push responses past the 24-hour window, a specialist can audit your message processing architecture and recommend optimizations such as priority queuing for time-sensitive conversations or a dedicated real-time path for first responses that bypasses slower batch processing. For businesses that routinely need to follow up with customers more than 24 hours after an initial contact, a specialist can design a compliant outreach strategy using WhatsApp's marketing and utility template categories that allows you to re-open conversations in a policy-compliant way. You should also seek specialist help if you are building an automated customer service system where the 24-hour session management logic needs to be deeply integrated with your CRM's conversation state and escalation workflows.
Conclusion
Error 63015 is a session window expiry that is resolved by implementing session window tracking in your application, switching to approved template sends when the 24-hour window has passed, and alerting agents before conversations approach expiry. If this error is blocking your production system, contact our team and we will diagnose and fix it within the hour.
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