Populate Retell dynamic variables with Google Sheets data for call handling

Overview - This workflow provides Retell agent builders with a simple way to populate [dynamic variables](https://docs.retellai.com/build/dynamic-variables) using n8n. - The workflow fetches user information from a Google Sheet based on the phone number and sends it back to Retell. - It is based on Retell's [Inbound Webhook Call](https://docs.retellai.com/features/inbound-call-webhook). - Retell is a service that lets you create Voice Agents that handle voice calls simply, based on a prompt or using a conversational flow builder.

Who is it for For builders of [Retell's](https://www.retellai.com/) Voice Agents who want to make their agents more personalized.

Prerequisites - Have a [Retell AI Account](https://www.retellai.com/) - [Create a Retell agent](https://docs.retellai.com/get-started/quick-start) - [Purchase a phone number](https://docs.retellai.com/deploy/purchase-number) and associate it with your agent - Create a Google Sheets - for example, [make a copy of this one](https://docs.google.com/spreadsheets/d/1TYgk8PK5w2l8Q5NtepdyLvgtuHXBHcODy-2hXOPP6AU/edit?usp=sharing). - Your Google Sheet must have at least one column with the phone number. The remaining columns will be used to populate your Retell agent’s dynamic variables. - All fields are returned as strings to Retell (variables are replaced as text)

How it works - The webhook call is received from Retell. We filter the call using their whitelisted IP address. - It extracts data from the webhook call and uses it to retrieve the user from Google Sheets. - It formats the data in the response to match Retell's expected format. - Retell uses this data to replace [dynamic variables](https://docs.retellai.com/build/dynamic-variablesdynamic-variables) in the prompts.

How to use it See the description for screenshots! - Set the webhook name (keep it as POST). - Copy the Webhook URL (e.g., https://your-instance.app.n8n.cloud/webhook/retell-dynamic-variables) and paste it into Retell's interface. Navigate to "Phone Numbers", click on the phone number, and enable "Add an inbound webhook". 

- In your prompt (e.g., "welcome message"), use the variable with this syntax: {{variablename}} (see [Retell's documentation](https://docs.retellai.com/build/dynamic-variables)). 

- These variables will be dynamically replaced by the data in your Google Sheet.

Notes - In Google Sheets, the phone number must start with '+. - Phone numbers must be formatted like the example: with the +, extension, and no spaces. - You can use any database—just replace Google Sheets with your own, making sure to keep the phone number formatting consistent.