I saw this marked as a solution. Can you please provide some tested examples?
The transfer number field supports dynamic variables (substituted at runtime), but the extension field has a strict format requiring only 0-9, *, # — so it doesn’t accept dynamic variables directly. Same likely applies to the IVR navigation prompt being a static field.*
A workaround: put the extension digits as part of the SIP URI / number, or use a dynamic variable for the entire transfer destination. For example, build a dynamic variable that contains the full target (number + extension formatting handled upstream), and reference it in the transfer number field.
If you need true dynamic extension/IVR-prompt selection, consider using multiple transfer nodes (one per extension) in a Conversation Flow and route via transition conditions, or use agentic warm transfer where a transfer agent navigates the IVR conversationally.
Could you please explain in more detail what you’re trying to achieve? This will help us better understand your use case and assist you more effectively.
Clarification: Retell does accept dynamic variables, but keep in mind: the resolved value must contain only ‘0-9’, ‘*’, and ‘#’; Retell does not support the Twilio ‘W’. If the Mitel auto-attendant needs a delay before accepting digits, the cleanest pattern is to put a short conversation node (with “skip response” enabled) before the Call Transfer node so the agent waits for the IVR prompt — instead of trying to encode WWW into the digit string.