An invoice is simple. Put your name and contact, the brand and contact, an invoice number and date, a line for each deliverable with the agreed fee, the total, payment terms like net 30 and a due date. Add how you want to be paid. Agree the fee and terms in writing before you start so the invoice holds no surprises.
What a creator invoice needs
Clear and boring is good. An invoice should be easy to approve.
Deliverables and fee
One line per deliverable with the agreed amount, then the total.
Payment terms
State net 15 or net 30 and your accepted payment method.
Send it on time
Invoice the day you deliver. Late invoices get paid late.