n8n Data Mapping Problems: Why the Next Node Receives the Wrong Values

The data mapping flow you are debugging

Data flows from one node to the next through input and output items. Wrong mapping happens when an expression references the wrong field, a nested object is accessed incorrectly or a field name changed. The source value is correct but the next node receives the wrong value. Find where the correct source value becomes an incorrect value passed to the next node.

What to check first

Correct source but wrong passed value

First confirm the source value is correct in the output of the previous node. Then check the expression on the next node that references it. If the value is correct in the output but wrong in the next node, the expression is the problem. The expression references a field incorrectly, accesses a nested object at the wrong path or uses a field name that changed.

Expressions and field references

n8n uses expressions to pass values between nodes. An expression references a field from the input items. If the field name in the expression does not match the actual field, the value is wrong or empty. Check the expression against the actual field names in the input items. Field names are case sensitive and must match exactly.

Nested objects and arrays

Values inside nested objects or arrays need the correct path in the expression. If the expression points to the wrong level of the structure, the value is wrong even though it exists in the data. Inspect the JSON structure of the input items and confirm the expression accesses the correct path. Nested data and arrays are a common source of mapping errors.

Field names that changed

If a field was renamed or removed in the source, the expression that references the old name returns nothing or an error. Check whether the field still exists in the input items under the name the expression uses. A field rename in an upstream node or the source application breaks every expression that references the old name.

Null values and empty fields

An expression that references an empty field returns null or an empty value. If the next node expects a value and receives null, it can fail or produce wrong output. Check whether the source field is genuinely empty before treating it as a mapping problem. Add null handling in the expression if the field can be empty.

How to test it

1. 1.Check the output items of the previous node for the correct value.
2. 2.Check the expression on the next node that references the value.
3. 3.Confirm the field name in the expression matches the actual field.
4. 4.Check nested object paths if the value is inside an object.
5. 5.Check for null values and add handling if needed.
6. 6.Run the workflow and check the input items of the next node.