Thank you so much.
This was very useful, and I already made it work on my end. I share what I did for the workflow in case someone is in the same situation. I firts generated a pdf. I then send the email with the params I need to send, that includes the pdf encoded in base64.
This is the structure of the JSon. Ignore the dataVariables if that is not your case.
The filename value is the name of the pdf you want to give and the content is the type. I used “application/pdf” which is the MIME type of the file.

It works just fine. I hope it helps