how can I sell items to the supplier with one invoice
I think your question is incomplete. As you have written it, it is self-answering: you sell items to anyone with one invoice by putting them all on one sales invoice.
I suspect what you are really asking is how to offset simultaneous purchase and sales invoices from/to the same business. That is, what do you do when a supplier buys something from you. The answer is found in the Guides, with illustrations: Offset simultaneous sales and purchase invoices | Manager.