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Linq Sandbox

The Linq sandbox lets you build and test your iMessage integration against the real API — for free — before going live. You get a real phone line, full API access, and 7 days to validate your integration.

What Is the Sandbox?

The Linq Sandbox is a free trial period where you can test out iMessage and how it works for 7 days before committing to a subscription. In no way is a sandbox meant for full production accounts.

Getting Started

  1. Fill out the signup form (name, business email, phone, company) and tap Get Started

    Screenshot 2026-09-17 at 11.52.41 AM
  2. Complete the 4-step onboarding walkthrough
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    Screenshot 2026-09-17 at 11.54.00 AMScreenshot 2026-09-17 at 11.54.05 AM

Your credentials:

Token

Purpose

Partner API token

Every /v3 call — send as Authorization: Bearer <token>

Sandbox signup token

Completes signup only; expires in 1 hour, cannot call the API

Web session token

Signs you into the web app; not an API credential

Note: No token yet? Your phone line hasn't been assigned. It appears automatically once a line is allocated — no action needed.

The One Rule That Will Surprise You

In sandbox, you cannot start a conversation. You can only reply to someone who has already messaged your line first.

Before your first API call: text your sandbox number from your own phone. That inbound message unlocks replies to that number.

Sending to a number that hasn't messaged you returns:

HTTP 403  {"code": 2008, "message": "Recipient not allowed"}

Important notes:

  • For group chats, every participant must have messaged your line first — one unknown number fails the whole request
  • No time limit — any inbound message, however old, qualifies that number permanently
  • The rule applies when adding participants too, not just on initial send
What You Can Test

Sandbox messages are real — sent to real devices. Test with your own number or a colleague's.

  • Inbound messages
  • Replies, webhooks & real-time event logs
  • Read receipts & typing indicators
  • Tapback reactions
Rate Limits

Sandbox has two additional account-wide caps that production accounts do not:

Limit

Value

Messages per minute (all lines)

30

Messages per day (all lines)

7,000 — resets midnight UTC

Exceeding either returns HTTP 429 with a Retry-After header. Use exponential backoff. Only sends count — reads do not.

Trial & Going Live

The 7-day trial starts when your phone line is assigned — not when you sign up. At expiry, your token stops working and every call returns HTTP 401. Your account and history are not deleted.

Note: Webhook subscriptions are removed shortly before expiry. If deliveries go quiet slightly before your end date, that's expected — not a delivery fault.

Going live is simple — nothing breaks:

  • Your API token stays the same
  • The inbound-first rule is lifted
  • Sandbox rate limits are removed
  • Your phone number and message history carry over

One thing to redo: Re-register your webhook subscriptions pointing at your production endpoints.

Frequently Asked Questions

Why can't I send a message to a new number? In sandbox you can only reply — not initiate. Text your sandbox line from that number first, then try again.

Why do I have no API token? Your phone line hasn't been assigned yet. It will appear automatically — usually within minutes of signup.

Everything is returning 401. What's wrong? Your trial has likely expired. Your account and data are intact — upgrade to production to restore access.

I'm hitting 429 sooner than expected. Why? The 30/min cap is account-wide, not per line. Sends across multiple lines share the limit.

Does going live require new credentials? No. Your API token stays the same — sandbox restrictions are simply lifted from it.

Issues not covered here? Contact support@linqapp.com.