Posting CxML Invocie from postman with PDF attachment to SAP Ariba Procurement

I americium looking for an inputs however to station cxml invoice with attachment from postman to ariba procurement. I saw the papers which is mentioned below
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<Attachment>

<URL>cid:[email protected]</URL>

</Attachment>

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How tin I encode oregon make URL with cid URL>cid:[email protected]</URL> to update the cxml payload

Thank you.