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n8n "JSON parameter needs to be valid JSON": what it means and how to fix it

You see: JSON parameter needs to be valid JSON

What it means

A node (usually HTTP Request or Set) has a JSON field whose text is not valid JSON once n8n has filled in any expressions. The usual causes are a trailing comma, single quotes, an expression that puts a value with quotes or line breaks inside a string, or a value that is empty so the field reads {"name": }.

How to fix it

1. Open the failing node and look at the JSON field. Copy what the field resolves to (run the node once, or hover over the expression) into a JSON checker and read where it breaks.
2. Wrap any expression that fills in text in JSON.stringify so quotes and line breaks are escaped for you, for example {{ JSON.stringify($json.message) }}, and leave the quotes off around it.
3. Remove trailing commas and use double quotes only. If a value can be empty, give it a default, for example {{ $json.name ?? '' }}.
4. Run the node again with Execute node, then run the whole workflow.

If it keeps coming back

If it only breaks for some items, one of them has a value you did not plan for (an empty field, a line break, a quote). Pin that item's data on the node and test with it.

The One-Time Fix covers one workflow. What you send and what you get back.

Sources

• Expressions (n8n docs)