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The attribute is required but missing (cvc-complex-type.4)
The message
libxml2 (Python lxml, PHP, xmllint, this site):
Element 'H': The attribute 'req' is required but missing.
Java / Xerces:
cvc-complex-type.4: Attribute 'ccy' must appear on element 'Amount'.
What it means
The schema declares an attribute with use="required" and the element does not carry it.
Typical causes
- The attribute was written on a different element (parent or child).
- A typo in the attribute name, or different case.
- The exporting code skips attributes whose value is empty.
Example
Schema:
<xs:attribute name="ccy" type="CurrencyCode" use="required"/>
Document:
<Amount>100</Amount> <!-- needs ccy="EUR" -->
How to fix it
Add the attribute with a valid value.
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