stripe seat based billing prorate seats add remove

Adding seats now, removing them at renewal

Seat increases prorate immediately; seat decreases must wait for period end -- refunding mid-cycle desyncs billing from the entitlements it's supposed to gate (D11).

This is one of the things SaaS Billing + Tax Core already handles. Charge per-seat subscriptions: upgrades, downgrades, failed cards, invoices and sales tax.

Buy for $1493 of 3 clean-room builds passed · full refund if it fails on your machine

Is this you?

Seat count changes need the same asymmetric handling as plan changes: adding a seat mid-cycle should bill the prorated difference now, but removing a seat mid-cycle should not refund immediately -- the team already used those seats. Code that treats seat add and seat remove symmetrically either fails to charge for the seats actually used, or issues refunds the business didn't intend to give.

Why this one is easy to get wrong

Seats look like a simple quantity field on a subscription item, so it's tempting to write one updateSeats() function that always calls the same Stripe update with the new quantity -- the asymmetry (immediate for increases, scheduled for decreases) isn't visible from the Stripe API shape itself, only from the architecture decision that says which direction gets which treatment.

What you get instead

D11 pins seat increases to the same immediate-update, always_invoice path as an upgrade, and seat decreases to the same scheduled-at-period-end path as a downgrade, reusing D10's existing-schedule rule so a decrease never creates a second schedule. Decreases below the currently occupied seat count, and increases above a plan's maxSeats, are rejected before any Stripe call runs -- billing must not desync from entitlements.

Source: ARCHITECTURE.md D11 — checkable in the pack you receive

How you actually use this

You don’t install a library or wire up an SDK. Your own coding agent builds the code in your project, and you keep it — no runtime dependency on us.

Step 1
Download and unzip
You get a folder: the docs that tell an agent what to build, a starting skeleton, and the test suite that decides when it's done.
Step 2
Open it in Claude Code or Cursor
Point your coding agent at the folder. Nothing to install, no account with us, no API key.
Step 3
Paste one prompt
The pack contains the exact prompt. Paste it as your first message and leave it alone — it works through the build itself, choosing a cheaper or stronger model per task.
Step 4
Run ./verify.sh
One command. It prints a pass or fail for every check. Green means the build is done — the same script we ran to produce the receipt on this page.

Typical build: about 18 minutes of your agent working, mostly unattended. Then you integrate the working module into your app the way you would any code you’d written yourself.

Why you can believe this

3 of 3 runs passed

We ran this pack from an empty folder 3 times and published exactly what happened — every check, the model, the token cost, the wall time. Not a testimonial, and not our opinion: the same verify.sh you run yourself. Read the full receipt →

Buy for $149 14-day refund if verify.sh fails →