Square Payments Gateway for Sliced Invoices (WordPress Plugin)

WordPress Plugin for Sliced Invoices

Square Payments Gateway for Sliced Invoices

Accept invoice payments through Square with embedded card fields, signed webhook confirmation, native Sliced Invoices payment recording, optional partial payments and refund management inside WordPress.

One-time purchase. Built for WordPress and Sliced Invoices.

Designed to feel native inside Sliced Invoices

The plugin adds Square card payments while keeping your existing invoice workflow clean, familiar and easy to reconcile. Completed payments populate the standard Sliced Invoices payment ledger and can update the invoice status automatically.

Embedded Square card fields

Clients enter their card details in fields provided by Square’s Web Payments SDK. Raw card details do not pass through your WordPress forms.

Native payment recording

Completed payments are recorded in the standard Sliced Invoices payment history with the Square transaction reference, amount, currency and status.

Signed webhook synchronization

Square payment and refund events are authenticated using the exact notification URL, raw event body and environment-specific signature key. Duplicate deliveries are safely ignored.

Duplicate-charge protection

Stable idempotency keys and server-side checkout validation protect payment retries from creating unintended duplicate charges.

Optional partial payments

Allow clients to pay part of an outstanding balance and define the minimum permitted percentage. The current balance and currency are validated again on the server before every charge.

Refund management

Issue full or partial Square refunds from the invoice editor. Refund responses are checked against the original payment before the Sliced Invoices ledger is changed.

Sandbox and production modes

Keep test and live credentials separate so you can validate checkout, webhooks and refunds safely before accepting real payments.

Security-conscious credential options

Store credentials through the WordPress settings screen or define them as wp-config.php constants for improved production secret management.

Why choose this Square gateway?

A focused Sliced Invoices integration

Built specifically for businesses that invoice through Sliced Invoices instead of forcing a full WooCommerce checkout into a client-payment workflow.

Accurate server-authorized payments

The browser is never trusted to decide the invoice balance. Invoice identity, checkout session, amount, currency and minimum partial-payment rules are verified server-side.

Clean operational records

Provider payment IDs, refund IDs, statuses and event fingerprints are stored in dedicated records while completed transactions remain visible in the familiar Sliced Invoices ledger.

Agency and service-business friendly

Ideal for agencies, consultants, freelancers and service businesses that send invoices directly to clients and want Square as a card-payment option.

Built for businesses that invoice clients directly

• Digital and creative agencies
• Consultants and professional services
• Freelancers and independent specialists
• Trades and field-service businesses
• Client portals and online invoice workflows
• Businesses already using Square for payment processing

Requirements

• WordPress 6.4 or newer
• PHP 8.1 or newer
• The free Sliced Invoices plugin installed and active
• A Square account and Square Developer application
• Square Application ID, Location ID, access token and webhook signature key
• A publicly reachable HTTPS website for webhook delivery

How it works

1. Install the plugin alongside Sliced Invoices.
2. Enter your Square Sandbox credentials.
3. Add the webhook URL shown by the plugin to your Square application.
4. Test payment and refund flows using Square Sandbox.
5. Add production credentials and enable live mode when testing is complete.

Important compatibility information

This release processes individual card payments. It does not include automatic recurring billing, saved-card charging, Square OAuth seller onboarding, Apple Pay, Google Pay or Cash App Pay. Generated recurring invoices can be paid individually, but partial payment is disabled when an invoice is detected as recurring.

Square Payments for Sliced Invoices by Inventiva is independently developed by Inventiva. It is not sponsored, endorsed or certified by Square, Block, Inc. or Sliced Invoices. Square is a trademark of Block, Inc. Sliced Invoices is a trademark of its respective owner.

Start accepting Square payments in Sliced Invoices

Give clients a straightforward card-payment experience while keeping payment confirmation, partial payments and refunds connected to your WordPress invoice records.