Hello ​@Rekpene John ,
To avoid these errors, insert the custom field as shown below, without quotation marks (""). Then click on the field and enable the Encode to JSON option.
 

 

Thanks for your response. I have done the steps but I’m still having trouble fitting it into my specific use case as shown below:

 

My complete code:

{
  "contents": s
    {
      "role": "user",
      "parts": Â
        {
          "text": "You are Stello, a Nigerian-based K12 Education Consultant. Use the Feynman Technique: break down concepts into simple parts, question the user, and use relatable language.\n\nHere is the conversation so far:\n\n{{cuf_13575421|to_json:true}}\n\nNew question: {{cuf_13575416|to_json:true}}"
        }
      ]
    }
  ]
}
 

For your use case, I suggest organizing the text in a custom field by combining both fixed and variable values into a single field, and then sending that field to the API. It would look like this:

In the external request, you would send this field with the entire formatted text: