---
title: "Check GST refund allocations in Codex"
seoTitle: "GST refund Codex plugin: install and use"
description: "Install the free Fast GST Refund plugin, check a receipt shared by two invoices, and use the result to review your working."
topic: "Prepare with Codex"
published: 2026-10-01
checked: 2026-10-02
order: 32
updated: 2026-10-02
---

Use the free Fast GST Refund plugin to check invoice-to-receipt allocations in Codex and retrieve preparation guidance for Statement 3 and Annexure B. Start with the fictional example below, then use the same steps with anonymous rows from your working file.

The plugin connects to Fast GST Refund without an account or API key. You need a Codex client that supports local plugin marketplaces; OpenAI documents this flow for Codex in the ChatGPT desktop app.

## Install the plugin

1. [Download Fast GST Refund for Codex, version 1.0.1](/downloads/fast-gst-refund-codex-1.0.1.zip).
2. Extract the ZIP into a new project folder. Keep `.agents` and `plugins/fast-gst-refund` together inside it. On macOS, press **Command–Shift–.** in Finder to show hidden folders.
3. Open the extracted folder as a trusted project in Codex and restart the desktop app.
4. Open the Plugins directory, select the local marketplace **fast-gst-refund-local**, and install or enable **Fast GST Refund**. Review the connection to `https://fastgstrefund.com/mcp` if prompted.
5. Start a new chat in that project.

The package includes the marketplace file used by [OpenAI's local installation instructions](https://developers.openai.com/plugins/build/plugins#install-a-local-plugin-manually).

## Check your first receipt allocation

Ask Codex:

> Use Fast GST Refund to check these anonymous allocations. Invoice row 1 is ₹5,000, invoice row 2 is ₹8,000, and receipt row 1 is ₹10,000. I allocated ₹5,000 from that receipt to each invoice. Show the remaining balances in rupees.

Expand the tool activity and look for `check_receipt_allocation`. With these fictional amounts, the expected result is:

| Record        |         Amount remaining |
| ------------- | -----------------------: |
| Invoice row 1 |           ₹0 outstanding |
| Invoice row 2 |       ₹3,000 outstanding |
| Receipt row 1 | ₹0 available to allocate |

The receipt is fully allocated. Invoice 2 has ₹3,000 outstanding, so that is the record to follow up.

To see an error result, ask:

> Check a separate example: invoice row 1 is ₹5,000, receipt row 1 is ₹4,000, and I allocated ₹5,000 from that receipt to the invoice.

The checker should flag the receipt as **overallocated by ₹1,000**.

## Get preparation guidance

For the records needed before filling Statement 3, ask:

> I export software services under LUT and am preparing Statement 3. Use Fast GST Refund to get a checklist of records and checks.

For a purchase-statement issue, ask:

> Use Fast GST Refund to explain what to check when Annexure B reports a duplicate document.

These requests retrieve a prepared checklist or troubleshooting steps with guide links. Use the [Statement 3 example](/guides/statement-3-worked-example/), [Annexure B example](/guides/annexure-b-worked-example/) and [upload-error guide](/guides/gst-refund-json-upload-errors/) to review the source explanation.

## Use your own figures

Give the remote checker row numbers and amounts. Keep the mapping to invoice numbers and bank references in your local working file, and keep taxpayer identifiers, document contents and credentials out of tool inputs.

Ask Codex to show the returned balances beside your row labels. Review the corresponding records and resolve differences before using the working for a claim. The [free preparation pack](/preparation-pack/) includes blank templates, an offline allocation checker and a review checklist.

## If the plugin does not appear

Confirm that `.agents/plugins/marketplace.json` and `plugins/fast-gst-refund/plugin.json` are inside the project folder you opened. Restart the app after extracting or updating the package.

To enable the plugin explicitly for a trusted project, add this entry to `.codex/config.toml`. Create the file if needed and preserve existing settings:

```toml
[plugins."fast-gst-refund@fast-gst-refund-local"]
enabled = true
```

Restart the app, then start a new chat. See [OpenAI's project plugin configuration](https://developers.openai.com/plugins/build/plugins#enable-or-disable-a-plugin-for-a-repo).

For help, send [support](/support/) your Codex version, tool name and error message. To connect another assistant, use the [MCP setup guide](/guides/gst-mcp-server/). The [privacy notice](/privacy/) explains request handling and the analytics opt-out.