UBL Invoice validation: Cannot find the declaration of element 'ubl:Invoice'

Question

I have a simple Invoice xml:

<?xml version="1.0" encoding="UTF-8"?>
<ubl:Invoice xmlns:ubl="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2" xmlns:cac="urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2" xmlns:cbc="urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2">
  <cbc:CustomizationID>urn:cen.eu:en16931:2017#compliant#urn:xeinkauf.de:kosit:xrechnung_3.0</cbc:CustomizationID>
  <cbc:ProfileID>urn:fdc:peppol.eu:2017:poacc:billing:01:1.0</cbc:ProfileID>
  <cbc:ID>RE-2024-03</cbc:ID>
  <cbc:IssueDate>2024-02-27</cbc:IssueDate>
  <cbc:DueDate>2024-03-28</cbc:DueDate>
  <cbc:InvoiceTypeCode>380</cbc:InvoiceTypeCode>
  <cbc:DocumentCurrencyCode>EUR</cbc:DocumentCurrencyCode>
  <cbc:BuyerReference>992-90009-96</cbc:BuyerReference>
  <cac:AccountingSupplierParty>
    <cac:Party>
      <cbc:EndpointID schemeID="9918">DE16520503531004885412</cbc:EndpointID>
      <cac:PostalAddress>
        <cbc:StreetName>Teichstr. 15</cbc:StreetName>
        <cbc:CityName>Berlin</cbc:CityName>
        <cbc:PostalZone>10232</cbc:PostalZone>
        <cac:Country>
          <cbc:IdentificationCode>DE</cbc:IdentificationCode>
        </cac:Country>
      </cac:PostalAddress>
      <cac:PartyTaxScheme>
        <cbc:CompanyID>279247134</cbc:CompanyID>
        <cac:TaxScheme>
          <cbc:ID>FC</cbc:ID>
        </cac:TaxScheme>
      </cac:PartyTaxScheme>
      <cac:PartyLegalEntity>
        <cbc:RegistrationName>PC Service GmbH</cbc:RegistrationName>
        <cbc:CompanyID>279247134</cbc:CompanyID>
      </cac:PartyLegalEntity>
      <cac:Contact>
        <cbc:Name>Max Siebert</cbc:Name>
        <cbc:Telephone>0312424323</cbc:Telephone>
        <cbc:ElectronicMail>max.siebert@pc-service-berlin.de</cbc:ElectronicMail>
      </cac:Contact>
    </cac:Party>
  </cac:AccountingSupplierParty>
  <cac:AccountingCustomerParty>
    <cac:Party>
      <cbc:EndpointID schemeID="9930">DE279247134</cbc:EndpointID>
      <cac:PostalAddress>
        <cbc:StreetName>Bergstr. 25</cbc:StreetName>
        <cbc:CityName>Frankfurt</cbc:CityName>
        <cbc:PostalZone>54632</cbc:PostalZone>
        <cbc:CountrySubentity>Hessen</cbc:CountrySubentity>
        <cac:Country>
          <cbc:IdentificationCode>DE</cbc:IdentificationCode>
        </cac:Country>
      </cac:PostalAddress>
      <cac:PartyLegalEntity>
        <cbc:RegistrationName>DB Service GmbH</cbc:RegistrationName>
        <cbc:CompanyID>DE279247134</cbc:CompanyID>
      </cac:PartyLegalEntity>
    </cac:Party>
  </cac:AccountingCustomerParty>
  <cac:Delivery>
    <cbc:ActualDeliveryDate>2024-02-24</cbc:ActualDeliveryDate>
  </cac:Delivery>
  <cac:PaymentMeans>
    <cbc:PaymentMeansCode>42</cbc:PaymentMeansCode>
    <cac:PayeeFinancialAccount>
      <cbc:ID>DE13520503531004885466</cbc:ID>
      <cbc:Name>Viktor Settel</cbc:Name>
      <cac:FinancialInstitutionBranch>
        <cbc:ID>HELADEF1KAS</cbc:ID>
      </cac:FinancialInstitutionBranch>
    </cac:PayeeFinancialAccount>
  </cac:PaymentMeans>
  <cac:TaxTotal>
    <cbc:TaxAmount currencyID="EUR">204.06</cbc:TaxAmount>
    <cac:TaxSubtotal>
      <cbc:TaxableAmount currencyID="EUR">1074.00</cbc:TaxableAmount>
      <cbc:TaxAmount currencyID="EUR">204.06</cbc:TaxAmount>
      <cac:TaxCategory>
        <cbc:ID>S</cbc:ID>
        <cbc:Percent>19.00</cbc:Percent>
        <cac:TaxScheme>
          <cbc:ID>VAT</cbc:ID>
        </cac:TaxScheme>
      </cac:TaxCategory>
    </cac:TaxSubtotal>
  </cac:TaxTotal>
  <cac:LegalMonetaryTotal>
    <cbc:LineExtensionAmount currencyID="EUR">1074.00</cbc:LineExtensionAmount>
    <cbc:TaxExclusiveAmount currencyID="EUR">1074.00</cbc:TaxExclusiveAmount>
    <cbc:TaxInclusiveAmount currencyID="EUR">1278.06</cbc:TaxInclusiveAmount>
    <cbc:AllowanceTotalAmount currencyID="EUR">0.00</cbc:AllowanceTotalAmount>
    <cbc:ChargeTotalAmount currencyID="EUR">0.00</cbc:ChargeTotalAmount>
    <cbc:PrepaidAmount currencyID="EUR">0.00</cbc:PrepaidAmount>
    <cbc:PayableRoundingAmount currencyID="EUR">0.00</cbc:PayableRoundingAmount>
    <cbc:PayableAmount currencyID="EUR">1278.06</cbc:PayableAmount>
  </cac:LegalMonetaryTotal>
  <cac:InvoiceLine>
    <cbc:ID>1</cbc:ID>
    <cbc:InvoicedQuantity unitCode="C62">2.000000</cbc:InvoicedQuantity>
    <cbc:LineExtensionAmount currencyID="EUR">934.00</cbc:LineExtensionAmount>
    <cac:Item>
      <cbc:Name>PC Fujitsu TX-23</cbc:Name>
      <cac:ClassifiedTaxCategory>
        <cbc:ID>S</cbc:ID>
        <cbc:Percent>19.00</cbc:Percent>
        <cac:TaxScheme>
          <cbc:ID>VAT</cbc:ID>
        </cac:TaxScheme>
      </cac:ClassifiedTaxCategory>
    </cac:Item>
    <cac:Price>
      <cbc:PriceAmount currencyID="EUR">467.000000</cbc:PriceAmount>
    </cac:Price>
  </cac:InvoiceLine>
  <cac:InvoiceLine>
    <cbc:ID>2</cbc:ID>
    <cbc:InvoicedQuantity unitCode="C62">2.000000</cbc:InvoicedQuantity>
    <cbc:LineExtensionAmount currencyID="EUR">140.00</cbc:LineExtensionAmount>
    <cac:Item>
      <cbc:Name>PC Installation</cbc:Name>
      <cac:ClassifiedTaxCategory>
        <cbc:ID>S</cbc:ID>
        <cbc:Percent>19.00</cbc:Percent>
        <cac:TaxScheme>
          <cbc:ID>VAT</cbc:ID>
        </cac:TaxScheme>
      </cac:ClassifiedTaxCategory>
    </cac:Item>
    <cac:Price>
      <cbc:PriceAmount currencyID="EUR">70.000000</cbc:PriceAmount>
    </cac:Price>
  </cac:InvoiceLine>
</ubl:Invoice>

And the following .xsd to validate it:

https://github.com/itplr-kosit/xrechnung-visualization/blob/master/src/xsd/xrechnung-semantic-model.xsd

Each time I try to validate the xml, it tells me:

11:76 cvc-elt.1.a: Cannot find the declaration of element 'ubl:Invoice'.

But if you look at the .xml, ubl:Invoice is present.

The .xml has to be in the format provided by xrechnung-semantic-model.xsd, in order for it to be processed by xr-pdf.xsl.