Incusia

Incusia is invoicing for solo freelancers and contractors. Every plan has unlimited invoices and clients, and the monthly price you sign up at is written into the Terms of Service, so it can't go up later. Send an invoice and see when it's delivered and opened. Reminders go out on their own, and clients pay by card, Apple Pay or bank transfer from a button on the invoice, with no login. Plans are $9 a month, $29 a month for Pro, or $99 once. 7-day trial with full Pro access, no card needed.