Hello Team, I need urgent assistance with the Native SMS feature (send_sms). I am encountering a blocking error where the system claims I am not on a phone call, despite the logs confirming otherwise. The Issue: My agent triggers the native SMS tool correctly, but the execution fails immediately with the error: Encountered error in sending SMS: SMS is only supported for phone calls Technical Context: Call Type: Real Inbound Phone Call (Physical Mobile Device calling the Purchased Retell Number). Log Evidence: The call logs clearly state the type is phone_call (NOT web_call), yet the tool rejects the SMS request. Setup: I am using the standard Native Function with "Static Sentence" content. Number Status: The phone number is active and purchased within Retell. My Questions: Bug Confirmation: Why does the system throw a "web call" error on a proven inbound phone call? Is there a backend restriction on my account or number? Best Practices: To rule out any configuration errors, could you confirm the ideal JSON definition for the parameters section when using "Static Sentence"? Prompting: Is there a specific instruction required in the System Prompt to ensure the LLM handles the tool execution status correctly? I have attached a screenshot of the log showing the contradiction (Call Type: Phone Call vs Error: Supported only for phone calls). Could you please investigate?

This looks like a context mismatch during tool execution, not a prompt issue. Even though the call is inbound and logged as phone_call, this error usually occurs when the SMS tool is triggered outside the active call context (e.g. after call state ends, async step, or delayed agent action). Native SMS can only execute while the call session is live. Key checks: • Ensure send_sms is triggered during the active call, not after a response completes • Avoid conditional or delayed tool calls • Use a minimal static payload (no dynamic fields) No special system prompt is required — this is not LLM behavior-related. If this still occurs, it’s likely a backend flag or account-level restriction, and Retell support will need to validate SMS enablement on your number. Happy to help verify your flow or narrow this down further.