Adds an attachment to an existing invoice. Do not confuse with add_attachments method (note plural)

curl -H "Content-Type: application/octet-stream"
            https://app.b2brouter.net/invoices/1/add_attachment.json?filename=test.pdf&key=xxxxx
            -X POST --data "@attachment.pdf"
curl --location --request POST 'https://app-staging.b2brouter.net/invoices/xxxx/add_attachment.xml?filename=file.pdf' \
--header 'X-B2B-API-Key: xxxxxxx' \
--header 'Content-Type: application/octet-stream' \
--data-raw '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'
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