You must use an xml format with specific fields, along with a certified email: Pec and an SDI number that identifies the program used and a digital signature that the program itself makes.
There is no space to write here, here are the details
https://www.fattureincloud.it/guida-fatturazione-elettronica/fattura-elettronica-come-funziona/

Thank you.
I think we need to implement the XML format.

There are already fields where you can add the PEc and SDI numbers.

Can you please test it out?
It's free to register, and you can set it up within 2 minutes.
And no credit card is required.

I look forward to getting your feedback.

Best,
Reza