Tax and VAT Collection
Collect the right billing evidence and let a tax provider work out the rate.
What it adds
Location and tax-ID capture at checkout, calculation delegated to the billing or tax provider, and evidence stored with the invoice.
What your agent is told to do
5
What your agent is told to do
5-
1
Never hard-code rates or maintain your own rate table. Rates change on political timetables and yours will be wrong within a year. Send the address, customer status and product type to the provider and use what it returns.
-
2
Collect the billing address and, for business customers, a tax ID. Validate the tax ID where the provider offers validation, but do not block checkout when the validation service is merely unavailable.
-
3
Store the evidence used for each transaction alongside the invoice: address, tax ID, validation result, rate applied, and the provider's decision. That is what an audit asks for, and it must reflect the moment of sale.
-
4
Decide whether displayed prices are tax-inclusive or tax-exclusive per market, and show the tax line separately on the invoice either way.
-
5
Handle reverse charge and exemption as provider-returned outcomes with their own invoice wording, not as a zero rate with no explanation.
Edge cases it handles
6
Edge cases it handles
6- A valid tax ID changes who owes the tax. An invalid or unverifiable one must not silently be treated as valid — decide the fallback and state it to the customer.
- A customer moving country mid-subscription changes the rate on the next invoice, not retroactively.
- Tax-inclusive display in one market and exclusive in another means the same plan shows different headline prices. That is correct; make the UI handle it.
- Proration and discounts are taxed too. The tax figure must come from the same provider call that produced the amount, not be added afterwards.
- Digital and physical products can be taxed differently at the same address. Send the product type; do not assume one rate per customer.
- Stored tax evidence has a legal retention period that usually outlives the customer's account. Deleting an account must not delete its invoices.
Definition of done
8
Definition of done
8- No tax rate is hard-coded anywhere in the codebase.
- Billing address is collected before purchase and tax ID collection is available for business customers.
- Each invoice stores the address, tax ID, validation outcome and rate used at the time of sale.
- Reverse charge and exemption produce their own explicit invoice wording.
- Inclusive and exclusive pricing are configured per market and the tax line is always itemised.
- Invoices and their tax evidence survive account deletion for the required retention period.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Usage Limits
Usage Limits
Cap what free accounts can do — visibly and fairly.
What it does
Per-plan usage limits, enforced server-side, with the user always able to see where they stand.
How it works
- 1 Define limits per plan in one place. Do not scatter magic numbers through the codebase.
- 2 Enforce on the server at the point of creation. A client-side check is decoration.
- 3 Show current usage BEFORE the user hits the wall — surprise limits feel like a bug.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/usage-limits
Upgrade Modal
Upgrade Modal
Sell the upgrade at the exact moment someone wants it.
What it does
A focused upsell that appears when a free user reaches for a paid capability.
How it works
- 1 Trigger it at the point of intent — when they click the locked thing — not on a timer or on page load.
- 2 Name the specific feature they just tried to use. A generic pricing modal converts far worse.
- 3 State the price plainly and give one button to upgrade.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/upgrade-modal
Billing Portal
Billing Portal
Let people manage their own subscription.
What it does
A billing area where users can see their plan, change payment method, get invoices, and cancel.
How it works
- 1 Use the payment provider's hosted billing portal if it has one. Do not rebuild card management — it's a PCI liability you don't need.
- 2 Show the current plan, renewal date, and payment method on your own account page.
- 3 Make cancelling possible without emailing support. Dark patterns here generate chargebacks.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/billing-portal
How it works
-
1
Copy the link
Grab the Markdown instruction URL for this feature.
-
2
Give it to your AI
Paste it into Claude Code, Cursor, v0, Lovable — whatever you build with.
-
3
It inspects, then implements
Your agent reads your existing app first, then adds the feature to fit it.
Works with your stack
These instructions are written to adapt. They tell the agent to detect your framework, match your existing design system, and reuse what you already have — rather than assuming a particular stack.
Need it tighter than that? Customize the feature and tell it exactly what you're running.