How to Choose a Payment Gateway: ECPay, TapPay, LINE Pay and Stripe Compared on Fees, Settlement and Self-Build vs SaaS

We want to take credit cards on our site — which one do we integrate? ECPay? Stripe? Or just LINE Pay? The most common pre-quote question. The cost of choosing wrong is concrete: a 0.5% fee difference on NT$1M monthly volume is NT$60,000 a year; a 5-day settlement gap is a cash-flow squeeze for a small shop. This piece puts Taiwan four most-used gateways on one table.

Fits vs Does-Not-Fit

When self-integrating a gateway fits:

You have a site/app and want checkout to stay on-site, owning member and order data.
You need subscriptions, installments or recurring charges requiring API-level control.
You want multiple payment methods (cards plus convenience store plus transfer plus mobile pay).

When it does not fit — use a platform first:

You sell a handful of items with single-digit monthly orders: Shopee/LINE Shopping or Shopify built-in payments are cheaper.
You have no engineering resources and will not outsource ops: self-built error-handling and reconciliation will crush you.
Your customers are mostly overseas and need multi-currency: lead with Stripe, not a local Taiwan gateway.

Alternatives Matrix

Option	Card fee	Settlement	Pros	Cons
ECPay	~2.0%–2.75%	~T+2 to monthly	Most complete Taiwan payments, great docs	Local only, weak intl cards/multi-currency
TapPay	Negotiated	By plan	Direct bank acquiring, great UX, custom checkout	Needs volume, more technical onboarding
LINE Pay	~2.0%–3.0%	By contract	Strong traffic, familiar to TW users, high mobile conversion	LINE-ecosystem centric, single method
Stripe	3.4% plus NT$10 (local card)	~T+7	Global multi-currency, best subscription/API, top docs	Few local TW methods, higher intl-card fees

In practice it is usually ECPay (local everything) plus Stripe (cross-border subscriptions) dual-track, not either/or.

Full Process Breakdown

Stage 1 Requirements and selection (3 to 5 days): Clarify methods, subscription/installments, amount tiers, cross-border. Deliverable: gateway recommendation plus fee model sheet. Tools: Notion / Google Sheet.
Stage 2 Application and review (1 to 3 weeks, the biggest bottleneck): Submit to the gateway, prepare business registration and compliance pages. Deliverable: an approved merchant account.
Stage 3 Integration (1 to 2 weeks): Backend creates orders, calls the API, handles callbacks and state machine. Deliverable: a testable checkout flow. Tools: Laravel plus queues.
Stage 4 Reconciliation and testing (3 to 7 days): Run success/failure/timeout in the sandbox, reconcile settlement files. Deliverable: reconciliation report plus error-handling checklist.
Stage 5 Launch and monitoring (ongoing): Small live test, add UptimeRobot monitoring and transaction alerts. Deliverable: go-live checklist.

Full Cost Breakdown

Development: single-gateway integration ~NT$30,000 to 80,000; multi-method plus subscription plus auto-reconciliation ~NT$120,000 to 250,000.
Processing fees: 2.0% to 3.4% per transaction — a recurring cost, not just the build.
Hidden costs: SSL (free via Let''s Encrypt; commercial EV ~NT$3,000 to 10,000/yr), some gateways monthly/account fees, cross-border FX loss and intl-card surcharges, retry-and-dispute handling labor.
Maintenance: API changes and regulatory updates need ongoing ops — a monthly maintenance plan is advisable.

Reality vs Client Imagination

Imagine: Payment integration takes a week. Reality: build is a week, but merchant review often takes 1 to 3 weeks, outside your control.
Imagine: Fees are all about the same. Reality: local vs international cards, 3D-secure, and industry category swing fees a lot.
Imagine: Once payment succeeds, we are done. Reality: reconciliation, refunds, chargebacks and timeout handling are where the real labor goes.

Common Traps × How to Avoid

Trusting only the front-end response: Always rely on the gateway server-side notification; the front end can be tampered with.
No idempotency: Callbacks can resend — use a unique key on order state to prevent double-crediting.
No failure testing: Test timeouts, cancellations, amount mismatches, not just success.
Hardcoding keys in front-end or repo: Keys go into env/secret management, never version control.
Ignoring refunds and invoicing: Plan refunds and e-invoicing together, or retrofitting hurts.

Success Metrics + 90-Day Roadmap

Day 30: Transaction success rate at least 98%, zero reconciliation gaps, no double-crediting.
Day 60: Analyze failure causes (card type, limits, 3DS), optimize checkout to reduce abandonment.
Day 90: Add subscriptions/installments or more methods; evaluate adding cross-border (Stripe).

Decision Checklist

☐ Do I need international cards / multi-currency?
☐ Do I need subscriptions, installments, auto-renewal?
☐ Do I need convenience-store codes / ATM transfer?
☐ What settlement cycle can my cash flow tolerate?
☐ Do I have engineering resources for callbacks and reconciliation?
☐ Do I need to keep checkout on-site?
☐ Can my monthly volume negotiate a lower rate?
☐ Are refunds, chargebacks and invoicing planned?

FAQ

ECPay or Stripe — which should I pick?

Depends on your audience. Mostly Taiwan with CVS/ATM/local cards, use ECPay; mostly overseas with multi-currency and strong subscription APIs, use Stripe. Many clients end up dual-track — ECPay for local, Stripe for cross-border.

Are fees negotiable?

Yes. Rates depend on your monthly volume, industry and chargeback ratio; enough volume earns negotiating room. Negotiate with real transaction tiers and compare two or three quotes.

Self-built gateway vs Shopify built-in — what is the difference?

Control and cost structure. Built-in is fast but fixed-fee with data on the platform; self-built costs more upfront but fees are negotiable and member/order data stays on your site — cheaper long-term, if you can maintain it.

What breaks most often after launch?

Reconciliation and callback handling. A payment-success screen does not mean funds arrived — always rely on the gateway server-side notification, and handle idempotency and timeout orders.

Call to Action

Want a which-gateways-for-your-category-and-volume model sheet, or to wire up payments plus reconciliation plus e-invoicing at once? ScriptWalker offers payment integration and e-commerce backend services, single-gateway integration from NT$30,000. Book a free 30-minute consult: