Best Payment Tools for SaaS MVPs

The pick isn't Stripe vs Paddle in the abstract — it falls out of who pays you and where they live. Three questions decide it:

• Are your buyers businesses or consumers? B2B buyers expect invoices, net terms, and seat-based or usage billing. Consumers expect a one-click checkout and a card form that feels native.
• Where are they? Selling to EU consumers means VAT on every sale. A merchant of record (Paddle, LemonSqueezy) absorbs that. Selling B2B in the US means state sales tax, which Stripe + a tax engine handles without giving up Stripe's billing model.
• How complex is your pricing? Flat monthly plans are easy everywhere. Trials, proration, add-ons, metered usage, and mid-cycle plan changes are where the tools diverge hard.

Answer those three before you read a single pricing page. The integration that matches your buyer beats the one with the nicer docs.

What actually bites you six months in:

• Webhook reliability and event coverage. Your whole access-control model hangs off subscription lifecycle events. Test what happens on a failed renewal, a dispute, and a downgrade.
• Proration and plan-change behavior. This is where billing bugs and angry refund emails come from. Read the exact proration rules, don't assume them.
• Tax handling that matches your buyers, not tax handling in general.
• Refund, dispute, and dunning flows — the unglamorous parts you'll touch constantly once real money moves.

What matters far less than the marketing implies:

• Raw transaction fee. A 0.5% difference is noise next to a week lost re-architecting a billing model that didn't fit. Optimize fees after product-market fit, not before.
• Number of supported payment methods. Most MVPs need cards and maybe Apple/Google Pay. Forty exotic local methods are a distraction at launch.
• Dashboard polish. You'll live in your own admin, not theirs.

The expensive ones, in order of how often I see them:

1. Trusting client-side payment state for access control. The browser says "paid," so the app grants the feature. Never do this — it's trivially bypassed. Gate access on the server, off a verified webhook, against your own database. On BookBed (booking SaaS on Flutter + Firebase + Stripe) the booking and entitlement state lives server-side and only moves on confirmed Stripe events, never on a client signal.
2. No idempotency on webhook handlers. Providers retry. If your handler isn't idempotent you'll double-provision or double-count. Store the event ID and skip duplicates.
3. Switching merchant of record after launch. Migrating live subscriptions between Stripe and Paddle is real work — exported customers, re-created subscriptions, re-mapped IDs. Decide the tax model up front.
4. Modeling pricing in code instead of in the billing provider. Hard-coded prices and plan logic scattered through the app means every pricing change is a deploy. Let the provider own products and prices.

Plenty of products are over-built on payments. You don't need the heaviest setup when:

• You sell one or two flat plans, or a one-time digital product. LemonSqueezy gets you live in an afternoon and covers tax as merchant of record. Reach for Stripe's full billing model only when you actually need usage-based or add-on pricing.
• You're pre-revenue and validating. Use Stripe Checkout (hosted) instead of a custom payment form. It's a fraction of the work and you can build a bespoke flow later if conversion data justifies it.
• You're B2B US-only. Stripe plus a sales-tax engine is enough — there's no reason to hand a merchant of record a cut for VAT you'll never owe.

The honest rule: pick the least complex setup that fits your buyer and pricing today, and design the webhook + server-side entitlement layer well enough that swapping providers later is annoying rather than catastrophic. Most of my SaaS work — Callidus (clinic SaaS, React + Firebase), Pizzeria Bestek (React + Supabase) — ships faster without agency overhead, precisely because the payment layer is kept boring and server-authoritative from day one.