Trouble Passing JSON Array to HTTP Node Placeholder

When inserting an array into your JSON body, one common pitfall is how n8n handles expressions within a JSON string. Here are a few steps to troubleshoot and resolve the issue:

1. Use Proper Expression Wrapping

If you’re using an expression (i.e. a placeholder) to insert your array, make sure you wrap your entire JSON with double curly braces. For example, instead of simply writing:

JSONCopied
{
  "corrections": {proposed_corrections}
}

wrap the whole JSON in an expression:

JSCopied
{{
  {
    "corrections": $json["proposed_corrections"]
  }
}}

This tells n8n to evaluate the expression and insert the array as valid JSON instead of leaving it as a raw string.

2. Check for Unexpected Control Characters

The error message “Bad control character in string literal” indicates that there might be hidden or unescaped control characters (like newline, tab, or carriage return) present in your JSON data. Double-check that:

• Any string values inside your array do not contain unescaped newline or tab characters.
• There are no extraneous characters introduced by copying or formatting from another editor.

3. Verify JSON Array Formatting

Ensure that your array is formatted correctly as valid JSON. For example, your array should look like this:

JSCopied
["value1", "value2", "value3"]

and not include extra commas or missing quotes:

JSCopied
["value1", "value2", "value3",]  // Incorrect: trailing comma

4. Use a JSON Validator

Even if you think the JSON is valid, pasting your JSON (or the output from your previous node) into a validator like JSONLint can help catch subtle issues.

Example Combined

If your previous node outputs an array under the key proposed_corrections, you can configure your HTTP Request node’s JSON body like this:

JSCopied
{{
  {
    "corrections": $json["proposed_corrections"]
  }
}}

This ensures that:

• n8n treats the entire body as an expression.
• The placeholder is properly replaced with your array.

By confirming that the expression is correctly wrapped, ensuring no unescaped control characters, and validating the JSON array syntax, you should be able to resolve the error.

Give these steps a try, and your workflow should process the array correctly in the HTTP Request node.