Missing child element(s)

A required child element is missing.

The message, as the validator reports it

Element 'order': Missing child element(s). Expected is ( qty ).

Why it happens

An element with minOccurs 1 (the default) that is not there.
The element is there but in another namespace, so it does not count.

How to fix it

Add the element the message names, in the position the schema's sequence gives it.

Example

Validated against order.xsd, below.

Reports the error

<order currency="EUR">
  <id>A-1</id>
</order>

Fixed

<order currency="EUR">
  <id>A-1</id>
  <qty>1</qty>
</order>

order.xsd

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="order">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="id" type="xs:string"/>
        <xs:element name="qty" type="xs:int"/>
        <xs:element name="status" type="Status" minOccurs="0"/>
        <xs:element name="code" type="Code" minOccurs="0"/>
        <xs:element name="note" type="Short" minOccurs="0"/>
      </xs:sequence>
      <xs:attribute name="currency" type="xs:string" use="required"/>
    </xs:complexType>
  </xs:element>
  <xs:simpleType name="Status">
    <xs:restriction base="xs:string">
      <xs:enumeration value="open"/>
      <xs:enumeration value="paid"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="Code">
    <xs:restriction base="xs:string">
      <xs:pattern value="[A-Z]{3}-[0-9]{4}"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="Short">
    <xs:restriction base="xs:string">
      <xs:maxLength value="10"/>
    </xs:restriction>
  </xs:simpleType>
</xs:schema>