Power Automate - Text Tags seem to disappear

Hello there,

I'm trying to upload a document, create an agreement and send for signature via cloud flow using Power Automate.

Simple test Word document with one text tag: 

Simple cloud flow:

The flow executes fine, the document is visible on the Sign portal:

But there is no email notification and the document in the portal seems to lack the text tags:

When I take the same document and start the sign process directly on the Sign portal with the "Send" menu option, everything looks fine:

Does anybody have any idea why this doesn't work with the cloud flow?

Thank you in advance.

Cheers,

David