How to add ZeroSettle to ChatGPT as a custom MCP plugin for your dot

Why connect ZeroSettle to a ChatGPT dot?

Dots are OpenAI's always-on agents inside ChatGPT, announced at DevDay on September 29, 2026. A dot has its own cloud computer and browser, keeps working between conversations, runs scheduled tasks, and reaches outside tools through ChatGPT plugins. Since October 28, 2026, some US Pro users can text their dot over iMessage or RCS through a third-party provider, Linq. But in OpenAI's words, "Your dot can only text you, and you're the only one who can text your dot."

Customers can text a ZeroSettle number instead. ZeroSettle gives your business a dedicated phone number on real iMessage, running on Apple hardware we operate in a server facility, with a REST API, signed webhooks, a hosted AI agent and an MCP server at https://portal.zerosettle.io/mcp. ZeroSettle is backed by Y Combinator and built by former Apple engineers. It isn't affiliated with or endorsed by OpenAI. Everything below about ChatGPT comes from the sources at the end, checked November 4, 2026.

The plugin gives your dot the owner's view of your number: who texted, what they said, and how the hosted agent is set up. The hosted agent or your own server still answers customers. For the bigger picture, see ChatGPT dots and iMessage.

What does OpenAI document, and what's only implied?

You can add ZeroSettle to ChatGPT with certainty. Whether your dot can call it is something you have to test, and that's what Steps 3 and 4 do.

What do you need before you start?

• Dot access and a plan with custom MCP. Dots are rolling out to Pro users 18 and older outside the EEA, UK and Switzerland, to Business Premium in supported regions (subject to workspace eligibility), and as an Enterprise/Edu/Healthcare beta an admin turns on.
• ChatGPT on the web. Custom MCP setup is web only, not in the mobile apps.
• A ZeroSettle number, if you're on Pro. Get it in the ZeroSettle console first. sign_up, set_profile and subscribe are write tools, so a read/fetch plugin can't run them.
• A phone that gets SMS, for the sign-in code.
• A decision about who answers customers. A new number starts managed by ZeroSettle's hosted AI agent, whose default business context is a made-up example. Write your own first (see the hosted AI agent guide), or set managed_by to "api" so your server gets the texts.

Step 1: How do you add the custom MCP server?

1. On ChatGPT in a browser, open Plugins and select +.
2. Choose Add custom MCP server. OpenAI's current help article says you don't need to turn on Developer Mode first.
3. Enter a name, such as ZeroSettle iMessage, and an optional description.
4. Under Connection, enter https://portal.zerosettle.io/mcp, including the /mcp. The server is public HTTPS, so skip the Secure MCP Tunnel option.
5. For authentication, choose OAuth and leave static client credentials empty. ChatGPT uses static credentials if you supply them, then a client ID metadata document (CIMD) if the server advertises one, otherwise dynamic client registration (DCR). ZeroSettle advertises DCR, so ChatGPT registers itself.
6. ChatGPT labels custom MCP servers Elevated risk. Tick I understand and want to continue.
7. Select Create as a plugin, then install the plugin.

ChatGPT supports SSE and streaming HTTP; ZeroSettle uses Streamable HTTP. Don't choose No authentication: ZeroSettle's /mcp needs the OAuth sign-in and doesn't read a token from the URL, so the token-in-the-URL trick some community projects use won't work.

Step 2: What happens when you sign in?

ChatGPT sends you to a ZeroSettle sign-in page on portal.zerosettle.io. Enter your phone number, then the SMS code. This is OAuth 2.1 with PKCE (S256), and ChatGPT gets its own token. ZeroSettle supports the refresh-token grant, which matters: OpenAI warns that without refresh, ChatGPT "may lose access after the original authorization expires."

Use the phone number you sign in to the ZeroSettle console with. It decides which account the plugin reaches; sign in with a different number and you reach a different account, which may have no ZeroSettle number at all.

What can each ChatGPT plan do with it?

There's a catch on both sides. Pro, the only plan with dot texting, can only read. Business and Enterprise can send, through a plugin an admin set up, but without dot texting. For sending through a dot, see approved replies on ChatGPT Business.

Which ZeroSettle tools are read-only?

OpenAI's developer docs say write actions need confirmation by default and tools without readOnlyHint count as writes. Here's how ZeroSettle annotates its tools:

On Business or Enterprise, create_api_key would put a fresh token into the conversation and clear_webhook would stop your server from hearing texts; neither belongs in a dot's daily work. ChatGPT asks you to confirm write actions by default, so read each confirmation before you approve it, and set your dot's rules (Step 4) so it asks before using ZeroSettle's write tools. See permissions and safety for dots and iMessage.

Step 3: Does your dot see the plugin?

OpenAI documents no separate MCP setup inside a dot. Its dots FAQ says: "Your dot can use your existing connections within the permissions you've granted." The getting-started article points to the dot's Customize > Plugins screen. Open it on desktop web and look for ZeroSettle iMessage; OpenAI doesn't say whether the mobile screen lists custom MCP plugins.

A listing is a good sign, not proof. learn.chatgpt.com limits dots to "supported plugins," and no OpenAI page says a custom MCP plugin counts. The next step settles it for your account.

Step 4: How do you test it safely?

Start with read-only calls, move to a send only if your plan allows writes, and stop at the first failure.

1. A read-only call. In a chat with your dot:
   prompt

   Use the ZeroSettle iMessage plugin to call get_line. Tell me my number
   and whether it's active. Don't call any other tool.

   If your dot reports your number, it can use the plugin. If it says it has no such tool, use ZeroSettle from a regular ChatGPT chat, where custom MCP is documented.
2. Read the conversations. "Use ZeroSettle list_conversations and list_messages and tell me who texted my number today. Don't reply to anyone."
3. Pro: confirm the limit. Ask the dot to text your own number with send_imessage. It shouldn't be able to. If the text goes through, don't treat the read/fetch limit as a guardrail.
4. Business or Enterprise: send only to yourself. "Use ZeroSettle send_imessage to text +1 (312) 555-0142 the words dot test. Show me the message first." Put your own number in place of the example. ChatGPT should ask you to confirm the write.
5. A scheduled run. Ask the dot to run get_line in a scheduled task tomorrow morning. OpenAI doesn't say whether scheduled tasks reach custom plugins.

Write down what passed, with the date; dots are new and may change. Your dot's Custom Rules offer four behaviors: Take action without asking, Take action if pre-approved, Ask before taking action, and Hand off to you. Give ZeroSettle's send and change tools "Ask before taking action." OpenAI doesn't say how Custom Rules treat custom MCP calls, so check that the rule stops a test send.

A first job: a weekday briefing

The job most likely to work on Pro uses only read-only tools. Dots run scheduled tasks; you give each one a time zone and an end date, and manage them under Scheduled:

Each weekday at 8 AM Pacific until December 31, 2026: use ZeroSettle
list_conversations and list_messages to summarize customer texts to my
number from the last 24 hours. List anyone still waiting on a reply.
If something looks urgent, DM me in Slack. Never send anything through
ZeroSettle.

It depends on tests 1 and 5 above passing. If the briefing comes back empty but the same prompt works live, the scheduled path is the problem. The morning summary guide covers this job, and Slack alerts for iMessage a route that doesn't need the plugin.

What can't a dot do with ZeroSettle?

• Reply to customers, or change the hosted agent, on Pro. Those are write tools.
• React to each text as it arrives. OpenAI's MCP Events can wake a dot, but ZeroSettle doesn't implement them, and OpenAI doesn't say whether personal custom plugins can use them. Real-time answers are the hosted agent's or your server's job. An untested stopgap: post ZeroSettle webhooks into a Slack channel and explicitly ask the dot to monitor it (adding a dot to a channel doesn't start monitoring).
• Text customers from the dot's own number. Dot texting is owner-only.
• Watch your number unprompted. No source says proactive research reads custom MCP plugins.
• Be set up from a phone, or use a static token. Setup is web only, with no bearer-token field.

Limits, consent and cost

ZeroSettle's limits apply whatever does the sending. On Pro, a number opens 5 new contacts a day (Growth: 25+ new outbound contacts a day); people who text you first, and ongoing conversations, don't count. Each number handles up to 10,000 messages a day with known contacts, and at most 2 messages to someone who hasn't replied. A customer who texts STOP (or a similar opt-out phrase, as the whole message or its first sentence) is opted out, and ZeroSettle blocks every number on your account from texting them. Only text people who asked to hear from you; cold messaging gets a line suspended. See iMessage and TCPA consent.

ZeroSettle Pro is $49 a month for one number, month to month, with a 30-day money-back guarantee. Growth starts at $199/month for one dedicated number, with 25+ new outbound contacts a day, and a Pro account can upgrade in the console. Need several numbers working as one? Multi-number Growth terms are agreed in an operator-priced invite, so talk to us. Enterprise is custom pricing through sales for high volume and compliance needs. See ZeroSettle pricing and which plan is right for you. On the ChatGPT side, the first dot is included in eligible plans; chatting with it doesn't count toward usage limits, but Work and Codex tasks do. OpenAI hasn't published terms beyond the first month's extended limits.

Troubleshooting

Using Claude or Cursor too? See connect Claude Code or Cursor to an iMessage number and the ZeroSettle connector for Claude Duet. Comparing the agents? Read ChatGPT dots vs Claude Duet vs Grok Bot for iMessage.