SQL Server – Resolve ‘XML Validation: Declaration Not Found for Element’ Error

I'm new to SQL Server and I have this task to complete (for learning purposes), yet I'm unable to figure out this error due to inexperience with XML Schemas (I think)

Here's what I'm trying to do –

1. Create a table with 2 columns – ID, XML info for some product (non-typed).
2. Add a row entry, that is, XML data for a product.
3. Create an XML Schema for the XML-product-data.
4. Bind this schema to the one (column) in the table.

I did this similar to what is mentioned here.

-- Create table ProductDocs
CREATE TABLE ProductDocs
(
    ID INT IDENTITY PRIMARY KEY,
    ProductDoc XML NOT NULL
);

-- Insert data into ProductDocs
INSERT INTO ProductDocs
(ProductDoc)
VALUES ('<Product>
            <ProductID>1</ProductID>
            <ProductName>Chai</ProductName>
            <SupplierID>1</SupplierID>
            <CategoryID>1</CategoryID>
            <QuantityPerUnit>10 boxes x 20 bags</QuantityPerUnit>\
            <UnitPrice>18.0000</UnitPrice>
            <UnitsInStock>39</UnitsInStock>
            <UnitsOnOrder>0</UnitsOnOrder>
            <ReorderLevel>10</ReorderLevel>
            <Discontinued>0</Discontinued>
        </Product>');


-- Create XML Schema
CREATE XML SCHEMA COLLECTION XS_ProductDoc 
AS '<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
               targetNamespace="http://www.microsoft.com/schemas/adventure-works/products"
               xmlns:prod="http://www.microsoft.com/schemas/adventure-works/products">

        <xs:element name="Product">
            <xs:complexType>
                <xs:sequence>
                    <xs:element ref="prod:ProductID" />
                    <xs:element ref="prod:ProductName" />
                    <xs:element ref="prod:SupplierID" />
                    <xs:element ref="prod:CategoryID" />
                    <xs:element ref="prod:QuantityPerUnit" />
                    <xs:element ref="prod:UnitPrice" />
                    <xs:element ref="prod:UnitsInStock" />
                    <xs:element ref="prod:UnitsOnOrder" />
                    <xs:element ref="prod:ReorderLevel" />
                    <xs:element ref="prod:Discontinued" /> 
                </xs:sequence>
            </xs:complexType>
        </xs:element>

        <xs:element name="ProductID" type="xs:integer" />
        <xs:element name="ProductName" type="xs:string" />
        <xs:element name="SupplierID" type="xs:integer" />
        <xs:element name="CategoryID" type="xs:integer" />
        <xs:element name="QuantityPerUnit" type="xs:string" />
        <xs:element name="UnitPrice" type="xs:double" />
        <xs:element name="UnitsInStock" type="xs:integer" />
        <xs:element name="UnitsOnOrder" type="xs:integer" />
        <xs:element name="ReorderLevel" type="xs:integer" />
        <xs:element name="Discontinued" type="xs:boolean" />

    </xs:schema>';

-- Bind the schema
ALTER TABLE ProductDocs
ALTER COLUMN ProductDoc xml (XS_ProductDoc);

But I'm getting this error –

XML Validation: Declaration not found for element 'Product'. Location:
/*:Product[1] The statement has been terminated.

Why is this error occurring?
And, how can I resolve it?