How do I fix "The attribute is not allowed"?

Remove the attribute, or declare it in the schema — those are the only two honest options. For genuinely extensible documents, declare so extensions are allowed by design. Check the spelling first: an unexpected attribute and a missing required one usually arrive together, and are the same typo.

XSD validation error

The attribute is not allowed

The document carries an attribute the schema never declared. XSD is closed by default: anything not named is forbidden rather than ignored.

Element 'order', attribute 'ref': The attribute 'ref' is not allowed. (line 2)

What it means

A complex type permits exactly the attributes it declares. Unlike a permissive JSON consumer, a schema validator does not skip what it does not recognise — an undeclared attribute is an error, even one that is obviously harmless.

This is the failure that appears when a sender adds a field. Their document is richer, yours is a validator, and the contract said no.

What usually causes it

A partner adding a field without a schema revision agreed on both sides.
Debug or trace attributes left on a document by a middleware layer.
A typo in an attribute name — the correct one goes missing and the misspelling is rejected as unknown.
A namespace-qualified attribute from an extension the schema does not import.

How to fix it

Remove the attribute, or declare it in the schema — those are the only two honest options.
For genuinely extensible documents, declare <xs:anyAttribute namespace="##other"/> so extensions are allowed by design.
Check the spelling first: an unexpected attribute and a missing required one usually arrive together, and are the same typo.

The same error elsewhere

libxml2 words these plainly. Xerces numbers them, and those cvc- codes are what most people end up searching for.

Xerces (Java)
cvc-complex-type.3.2.2: Attribute 'ref' is not allowed to appear in element 'order'.
.NET System.Xml
The 'ref' attribute is not declared.

Before and after

Both documents below are well-formed XML — that is the point. The test suite re-checks them against the real validator on every build: the first is confirmed to produce the exact message above, the second to validate cleanly.

Fails validation

<?xml version="1.0" encoding="UTF-8"?>
<order id="A-1" ref="X">
  <customer>Ada</customer>
  <issued>2026-01-31</issued>
  <state>open</state>
  <line>
    <code>AB-1234</code>
    <qty>2</qty>
  </line>
</order>

Validates

<?xml version="1.0" encoding="UTF-8"?>
<order id="A-1">
  <customer>Ada</customer>
  <issued>2026-01-31</issued>
  <state>open</state>
  <line>
    <code>AB-1234</code>
    <qty>2</qty>
  </line>
</order>

The schema both are checked against

order.xsd

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:simpleType name="status">
    <xs:restriction base="xs:string">
      <xs:enumeration value="open"/>
      <xs:enumeration value="closed"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="sku">
    <xs:restriction base="xs:string">
      <xs:pattern value="[A-Z]{2}-\d{4}"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="shortLabel">
    <xs:restriction base="xs:string">
      <xs:minLength value="3"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:element name="order">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="customer" type="xs:string"/>
        <xs:element name="middleName" type="xs:string" minOccurs="0"/>
        <xs:element name="nickname" type="shortLabel" minOccurs="0"/>
        <xs:element name="issued" type="xs:date"/>
        <xs:element name="state" type="status"/>
        <xs:element name="line" minOccurs="1" maxOccurs="2">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="code" type="sku"/>
              <xs:element name="qty" type="xs:positiveInteger"/>
            </xs:sequence>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
      <xs:attribute name="id" type="xs:string" use="required"/>
    </xs:complexType>
  </xs:element>
</xs:schema>

Check your own document ← All schema errors

Where this bites most

The terms behind it

Each of these is defined in one sentence and then demonstrated against the parser.

Complex typeA schema type for elements that have children, attributes, or both — everything a simple type cannot describe.

Other schema errors

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