The idea came from an interesting "tail wagging the dog" situation. I had an old domain (faxbeep.com) lying around unused which I'd been renewing for 20 years. When I finally built something there, I discovered users were more interested in a fax testing feature that I'd added as an afterthought - the abitlity to send a fax to our test numbers and see it appear on the website for 30 days.
That insight led me to dedicate faxbeep.com entirely to fax testing, and to buy payperfax.com for my original idea: straightforward, pay-as-you-go faxing. People still need to send faxes surprisingly often - for tax authorities, immigration paperwork, medical prescriptions, etc. The service charges a fixed fee for a 3-page fax (cover + 2 pages) with a bit more for additional pages, and you only pay if the fax sends successfully.
My current challenge is visibility - Google has essentially black-holed the site. Even exact match searches like [pay per fax] don't bring up the site. If anyone has SEO advice on how to climb out of this hole - I'd appreciate it!