FastSpring Platform Help

Step 1 — Gather context

If references/learnings.md exists, read it first for accumulated platform knowledge.

1. What are you trying to do?
   - A) Integrate the REST API (orders/subscriptions/products/accounts) or launch checkout
   - B) Build checkout — Store Builder Library (popup/embedded) or a hosted checkout session
   - C) Verify webhooks (X-FS-Signature HMAC-SHA256) and react to order/subscription events
   - D) Handle subscription lifecycle — dunning, overdue rebills, cancel/pause/resume
   - E) MoR concerns — tax/VAT remittance, refunds (fee is kept), payouts, chargebacks
   - F) Decide MoR (FastSpring) vs a raw processor, or compare to Paddle/Lemon Squeezy/Dodo

2. API or no-code? Code → REST API + SBL / webhooks. Low-code → hosted checkout + Zapier off webhooks.

Skip-ahead rule: if the user's prompt already provides enough context, skip to Step 2.

Step 2 — Route or answer directly

When routing, give the exact command, e.g. "This is a selection question — run: /sales-merchant-of-record FastSpring vs Paddle for a global SaaS".

Step 3 — FastSpring platform reference

Read references/platform-guide.md for the full reference — the MoR model (what FastSpring takes liability
for), capabilities + automation surface (API / webhook / UI), quote-based pricing + the refund-fee gotcha, the
data model, and quick-start recipes (provision on order.completed; sync subscriptions; SBL checkout).

Read references/fastspring-api-reference.md for the integration surface — base https://api.fastspring.com,
HTTP Basic auth (Developer Tools > APIs > API Credentials; password shown once), 250 calls/IP/min (429),
the endpoint catalog (products/offers/prices, orders, subscriptions, accounts, coupons, checkout sessions,
quotes, returns, events, webhooks), the Store Builder Library (Access Key), and HMAC-SHA256 webhooks
(X-FS-Signature, events array, dedupe on id) with the full event list.

Answer using only the relevant section. Don't dump the full reference.

Step 4 — Actionable guidance

Focus on the user's specific situation:

• MoR = FastSpring handles tax liability. It's the legal seller and remits global VAT/GST/sales tax — you
  don't register/file per jurisdiction. That's the reason to pick it over a raw processor, at a higher fee.
• Pricing is quote-based. Reported rates are 8.9% or 5.9% + $0.95, assigned by their sales team by
  transaction type + volume — no public rate card. Effective subscription rates can exceed 10–12%; model it.
• Refunds keep the fee. FastSpring retains its transaction fee on refunds — reconcile net revenue from
  return events; don't assume the fee reverses.
• Verify webhooks over the raw body. Set an HMAC secret, check X-FS-Signature (Base64 HMAC-SHA256), dedupe
  on event.id (redelivery happens), switch on event.type, return 2xx fast and process async.
• SBL for embedded checkout, API for server flows. Use the Store Builder Library (Access Key to sign carts) on
  the site; use the checkout-session / subscriptions endpoints server-side. FX refreshes every 6h → re-pull pricing daily.

If you discover a gotcha, workaround, or tip not covered in references/learnings.md, append it there.

Gotchas

> Best-effort from research (2026-07) — pricing is quote-based/negotiable and docs are largely JS-rendered; verify specifics in-account.

1. Pricing is quote-based, not public. ~8.9% or 5.9% + $0.95 assigned by sales; the pricing page shows
   no percentages. Get your rate in writing and model effective subscription cost (often 10–12%+ on small charges).
2. Refunds don't refund the fee. FastSpring keeps its transaction fee when you refund a customer — a top complaint.
3. Webhooks: verify X-FS-Signature over the RAW body. Signature is Base64 HMAC-SHA256; re-serializing the
   body before hashing is the common bug. Set a secret (verification is optional but treat it as mandatory).
4. Dedupe on event.id. Events can be redelivered; payloads carry created in milliseconds and an events array.
5. Enable webhook expansion if you need full JSON — otherwise events can carry references, forcing extra API reads.
6. Basic-auth password is shown once. Generate credentials in Developer Tools > APIs; store the password immediately.
7. Classic Commerce API is deprecated (moved to github.com/fastspring/fastspring-api) — build on the modern
   api.fastspring.com, not Classic.
8. MoR ≠ instant payouts. As seller of record, FastSpring pays out on a schedule — model cash flow.

Related skills

• /sales-merchant-of-record — Choosing a Merchant of Record across vendors (FastSpring vs Paddle/Lemon Squeezy/Dodo/Polar/Creem/Gumroad vs Stripe+Tax) — selection strategy, MoR-vs-processor tradeoffs
• /sales-paddle — Paddle platform help (MoR API/webhooks, Billing vs Classic) — the closest enterprise/B2B MoR alternative
• /sales-dodo-payments — Dodo Payments platform help (developer-first MoR — REST API, 9 SDKs, MCP server)
• /sales-checkout — Checkout/cart conversion strategy (order bumps, upsells, cart recovery) across platforms
• /sales-digital-products — Selling digital products (license keys, delivery, pricing) across tools
• /sales-do — Not sure which skill to use? The router matches any sales objective to the right skill. Install: npx skills add sales-skills/sales --skill sales-do -a claude-code

Examples

Example 1: Provision access when a purchase completes (developer/automation)

User says: "When someone buys my SaaS through FastSpring, how do I unlock their account automatically?"
Skill does: Points to a webhook listener on order.completed (and subscription.activated for
subscriptions): configure the webhook with an HMAC secret, verify the X-FS-Signature header (Base64
HMAC-SHA256) over the raw body, dedupe on event.id, then grant access from event.data. Notes returning
2xx quickly and processing async, and enabling webhook expansion for full payloads. References the Python
verification snippet in references/fastspring-api-reference.md.
Result: Authenticated, replay-safe automatic provisioning.

Example 2: Sync subscriptions to a CRM / warehouse via the API

User says: "I want a nightly job that pulls all my active FastSpring subscriptions into HubSpot."
Skill does: Uses GET /subscriptions with status=active&begin=&end=&live=true against
https://api.fastspring.com, HTTP Basic auth, backing off on 429 (250 calls/IP/min, no reset header —
exponential backoff). Maps account → contact/company and subscription → subscription object, and recommends
treating webhooks as the realtime signal with the daily API pull as reconciliation (FX refreshes every 6h).
Result: A resilient scheduled sync with rate-limit handling.

Example 3: MoR vs a processor — is FastSpring's fee worth it?

User says: "FastSpring quoted me around 8-9%. Stripe is way cheaper — why would I use FastSpring?"
Skill does: Frames the Merchant-of-Record tradeoff — FastSpring becomes seller of record and remits
global VAT/GST/sales tax (no per-country registration), whereas with Stripe you own tax compliance (Stripe Tax
calculates but doesn't remit). Flags FastSpring's quote-based rate (5.9%+$0.95 or 8.9%), the 10–12%+
effective subscription cost, and that refunds keep the fee, then routes the cross-vendor decision: "run:
/sales-merchant-of-record FastSpring vs Paddle vs Dodo for a global SaaS."
Result: A clear MoR-vs-processor decision grounded in tax liability + real effective fees.

Troubleshooting

My webhook signature verification fails

Symptom: Events arrive but X-FS-Signature never matches.
Cause: Hashing a re-serialized body instead of the raw bytes, the wrong secret, or no secret configured on
the webhook.
Solution: Compute Base64(HMAC-SHA256(raw_body, secret)) over the exact raw request body and compare to
X-FS-Signature with a constant-time check. Set the HMAC secret in Developer Tools > Webhooks; rotate it via the
"update a webhook key secret" API (validate the new key before discarding the old). Dedupe on event.id.

My API calls return 401 (or 429)

Symptom: Requests to api.fastspring.com are rejected.
Cause: 401 — bad/missing Basic auth (wrong store credentials, or the password wasn't saved when
generated) or a missing User-Agent header (mandatory). 429 — over 250 calls/IP/min.
Solution: Send Authorization: Basic base64(user:pass) with credentials from Developer Tools > APIs (the
password shows only once — regenerate if lost), always include a User-Agent, and use TLS 1.2+. On 429, back off
exponentially and batch by comma-separating IDs where supported.

Why did FastSpring keep its fee when I refunded a customer / why is my effective rate so high?

Symptom: Refunds cost you the fee, and subscription revenue nets far below the headline rate.
Cause: FastSpring retains its transaction fee on refunds, and the per-transaction component (5.9% + $0.95
or 8.9%) spreads poorly across small recurring charges, pushing effective rates to 10–12%+.
Solution: Reconcile net revenue from return/payout events (don't assume the fee reverses), get your
negotiated rate in writing, and model effective cost on your actual price points. If the fee structure doesn't fit
low-ticket subscriptions, compare alternatives via /sales-merchant-of-record.

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