A flat fee prices software as software. The platform costs the same in a month where you bill $50,000 as in a month where you bill $500,000, because the cost of running the infrastructure is broadly the same either way.
Flat fee models usually still carry a transaction fee, since card processing is a genuine variable cost. The distinction that matters is whether that variable component tracks processing cost or claims a share of your margin.
The practical test is what happens to your platform bill when you double your ad spend and it works. Under a flat fee the bill barely moves. Under a revenue share it doubles.
Flat fee is what makes marginal patients worth acquiring. When the platform takes a percentage, your contribution margin on patient one thousand is identical to patient one, so scale never improves your unit economics.
Flat fee pricing, in practice
Launch is $15,000 setup and $1,500 a month for 0 to 500 patients. Grow is $25,000 and $3,000 up to 2,000 patients. Scale is $50,000 and $5,000 up to 5,000. Transaction fees are 3%, 2% and 1.5% by tier. Every figure is published on the pricing page.