Sending invoices via Peppol works, the invoice PDF file is in the UBL
But any other attachments I have added to the invoice (I can see them when I click the attachment icon) are not in the UBL when I send the invoice via Peppol
So is it possible with Odoo to add something like a timesheet?
Other platforms add multiple invoices in the UBL, I have seen it in invoices from Billit
"Peppol multiple attachments" is not a question. A question is a substantial phrase that ends with "?"
We get close to 1,000 posts a month and not everyone will open a post to find out what your question is.
I have edited your post to make the title a question.
In the future, please consider (1) using a Question that makes it clear what you ask without requiring people to open your post and (2) adding Tags. This will often increase the chances people will respond and also make everything clearer for others who may come along later searching for the same thing.
Failing that, you can paste your future posts into an AI Chatbot and ask it to "please generate a question of no more than 16 words that summarizes what I am asking" and use that as your question.
See also https://www.odoo.com/forum/help-1/meta-why-do-some-questions-get-answers-and-others-do-not-25620