API: how can I download the e-invoice file in the same format that was delivered to the customer?

Hi,

for archiving reasons (as well as for cases where the customers call and ask for a "copy of the invoice") we would like to download the e-invoice file and upload it to our sales system which initiated the e-invoice process.

In order to send the customer manually a "copy of his invoice" via email in a format he can process, we would like to download the invoice in the same file format, he will get from b2brouter.

How can we find out, which file format will be used per invoice?

We can successfully download e-invoice files with the api endpoint "Get an invoice with a specific document type", but we did not find where we can see the file format the customer got from b2brouter.

Could you help us with that?

Thanks!