Open $portal_url and go to the billing or invoices page.

Instructions

Open $portal_url and go to the billing or invoices page.
Download every invoice dated in $month (format YYYY-MM) as a PDF.
Return each invoice: vendor, invoice_number, invoice_date, amount, currency, pdf_file.
Save each invoice keyed by vendor and invoice_number, so invoices saved in earlier runs are skipped.
If no invoice exists for $month yet, finish with an empty result and say so.

You provide “portal_url”, “month” each time you run it.