Building AI Receptionist ↔ POS Integrations: A Technical Guide

If you're building (or evaluating) an AI voice agent that takes orders or bookings, the POS integration is where the rubber meets the road. A voice agent that can't push data into the business's existing system is just a fancy answering machine.

Here's what we learned integrating with Toast, Square, Lightspeed, Epos Now, and Clover.

The Architecture

Phone Call → Voice AI (STT + NLU + TTS)
                ↓
         Order/Booking Object (structured JSON)
                ↓
         POS Adapter Layer
                ↓
    Toast API / Square API / Lightspeed API / etc.
                ↓
         Kitchen Display / Calendar

The adapter layer is key. Each POS has its own API quirks, auth flows, and data models. You don't want your voice AI logic coupled to any specific POS.

Key Technical Challenges

1. Menu Sync

POS menus change constantly. You need a polling or webhook mechanism to keep the AI's knowledge of available items, prices, and modifiers current. Stale menus = wrong orders = angry customers.

2. Real-Time Availability

Some items sell out. The AI needs to know mid-shift that the fish is gone. This requires either real-time inventory webhooks or a periodic sync with graceful fallbacks ("Let me check... I'm sorry, we're out of cod tonight. Can I suggest haddock?").

3. Modifier Handling

"Large chips, extra salt, no vinegar" — modifiers are where POS integrations get messy. Toast handles them differently from Square. Your adapter needs to normalise modifier structures.

4. Payment Flow

For phone orders, you typically have two paths:

• Pay on collection/delivery — simpler, just push the order
• Pay now by card — requires PCI-compliant payment link via SMS, adds complexity

5. Error Handling

What happens when the POS API is down? Your AI agent needs graceful degradation — take the order, store it, and retry. Never lose an order.

POS-Specific Notes

POS	API Quality	Auth	Gotchas
Toast	Good REST API	OAuth 2.0	Menu structure deeply nested
Square	Excellent	OAuth 2.0	Catalog API is powerful but complex
Lightspeed	Decent	API key	Rate limits tight on restaurant plan
Epos Now	Basic	API key	Limited webhook support
Clover	Good	OAuth	Sandbox ≠ production behaviour

What This Enables

When the integration works well:

• Phone order → appears on kitchen display in <3 seconds
• Booking call → appears in calendar instantly
• Customer confirmation SMS sent automatically
• Zero manual data entry
• 90% reduction in order errors

The businesses seeing the most value are high-volume food businesses (takeaways, chippers, pizza shops) where phone orders are a significant revenue channel and staff are too busy to answer every call.

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We built this integration layer at VoiceFleet for Irish restaurants and service businesses. Happy to answer questions in the comments.