[10 hours spend😵] E-conomic “Create a Booked Invoice” failing: [400] Validation failed. No lines on invoice

[Mads_lyngo]

Goal

Create a booked invoice in E-conomic via Make (without sending email—Likvido handles sending). The customer already exists in E-conomic. The invoice has one fixed product, quantity 1, price 5000, and a dynamic heading from monday (Destination + Departure month).

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Setup (short)

• Trigger: monday – Watch Board’s Column Values

• Fetch item: monday – Get an Item

• Router: filter for existing customer

• Lookup in E-conomic: E-conomic – Search Customers (Search filter = Email, Search term = email from monday)

• Create invoice: E-conomic – Create a Booked Invoice

  • Customer Number mapped from Search Customers

  • Heading: “Afrejse til {{Destination}} | {{Departure Month}}”

  • Line Items: Map = OFF on the Line Items section, and inside it a single Item 1:

    • Product = Product Number 2 (or mapped from Get Product → Product Number)

    • Quantity = 1

    • Unit Net Price = 5000 (plain number)

    • Line Description = “Depositum for afrejse” (optional)

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The issue

Some runs succeed, but quite often Create a Booked Invoice fails with:

[400] Validation failed. 1 error found. No lines on invoice.

In the module inspector Input I sometimes see lineItems is empty (even though “Item 1” is filled). Other times it’s populated and the run succeeds.

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Example payloads

Successful run:

[
  {
    "lineItems": [
      {
        "quantity": 1,
        "lineNumber": 1,
        "description": "Example product description",
        "unitNetPrice": 5000,
        "productNumber": "P001"
      }
    ],
    "notes_heading": "Example heading | October 2025",
    "customerNumber": 1234
  }
]

Failing run (lineItems missing):

[
  {
    "notes_heading": "Example heading | October 2025",
    "customerNumber": 1234
  }
]

---

Questions for the community

1. Are there known pitfalls with Line Items in “Create a Booked Invoice”, where Item 1 gets dropped if the top section has ever been set to Map = ON?

2. Is the “safe” approach to always keep Map = OFF on Line Items (top) and then add Item 1 manually?

3. Does the Product Number field have strict type requirements (string vs. number) to avoid the line being discarded?

4. Is there a way to “lock” Item 1, so Make won’t clear it during execution?