How to send the Italian XML E-Invoice as a byte array to a service provider webservice using CMK?

Summary:

Is it possible to send the italian compliant receivables XML invoice as a byte array to a service provider's web service using CMK?

Content (please ensure you mask any confidential information):

We currently are working with a service provider to generate the XML invoice and deliver it to the SDI tax authority, but this process had been doing it manually. So, we are working on the integration with the service provider as they will need to add the digital sign to the XML.

The problem is that the only option to send the data to the service provider is through a soap webservice call, and include the XML invoice as an attribute of the payload in a byte array. Is possible to achieve this with CMK setup or any other option?