Exam appointments are schedule, paid for, and taken through authorized test delivery providers (TDP's) and F5 is not a direct party to these transactions. F5 does not have any records of transactions, cannot provide refunds, and is not capable of creating or sending receipts or invoices for these transactions.
Typically, when you schedule and pay for your exam, the TDP will provide some form of receipt or confirmation. If this is insufficient to satisfy your needs, you must contact the TDP directly to get a receipt or invoice that meets your needs.
For Pearson VUE: https://www.pearsonvue.com/f5/contact/
For Exam Studio Online (ESO for Practice Exams only): mailto:firstname.lastname@example.org