Last updated 3 months ago

Reference Implementation

The reference implementation can be used to help you understand how Fast communicates with the Seller backend.
Included is a Python web application which implements the same endpoints a Seller would implement when integrating with Fast:


There is also a Postgres DB container which contains a couple sample products (this mimics the backend a seller would have)
It also contains a container for localtunnel which is used to expose your localhost to the internel using a simple URL.


Docker and Docker Compose

You will need Docker and Docker Compose to run the containers.


Docker Compose comes with the Docker installation on MacOS and Linux


1. Clone Repo

You will need to clone the reference implementation repository on your machine.

git clone
cd di-reference-implementation

Alternatively you can directly download the project as a zip file here

2. Setup .env file

We will be using localtunnel to expose the server running on your localhost to the internet.
To configure a static URL you will need to update the variable LOCALTUNNEL_SUBDOMAIN in the .env file to something unique.


Please make sure to edit this field, if you use LOCALTUNNEL_SUBDOMAIN=direferenceimplementation you will get errors.

When localtunnel runs it will take the value in LOCALTUNNEL_SUBDOMAIN and create the URL: https://<LOCALTUNNEL_SUBDOMAIN>

3. Setup Seller App in Sandbox

Next you will setup your sandbox application.
Navigate here to begin setup.

  1. Homepage

    • Enter your name and email and click Fast Login
  2. Org Details

    • Enter your relevant Org details including name, address, and phone number
  3. Store Details

    • Enter your website, name of business, and country
  4. Platform

    • Make sure to select Direct API here
  5. Install Fast Checkout

    • In the Rest API URL field, input the localtunnel address you create above. (should be https://<LOCALTUNNEL\_SUBDOMAIN> where <LOCALTUNNEL\_SUBDOMAIN> is equal to the value you put in the .env file)
    • Copy your App ID and put it somewhere safe (you will need this later)
    • Copy your Token and put it somewhere safe (you will also need this later)
  6. Business Verification

    • Select - Skip for now

4. Start Application

  1. Open a terminal window and run docker-compose up

Your logs should look something like this:

Make sure that the log for localtunnel that says your url is: matches the url you put in the Rest API URL while onboarding. If it does not match please navigate to step 1 to review how it's done.

5. Setup Fast Test Suite CLI

Now that the application is running, you can use the Fast Test Suite CLI to make calls to the Fast backend, which will then call your Seller Application running locally.
Please navigate here to get the CLI setup. Make sure to have your App ID and Token from onboarding handy, as they will be required to run the CLI.
NOTE: You will need to open a new terminal window/tab to run the CLI.

Once the Test Suite CLI is setup, you can run these commands:

./fast-test-suite login

./fast-test-suite pdp-simple-new-user --product-id=123 --app-id=<your-app-id>

./fast-test-suite pdp-simple-existing-user --product-id=123 --app-id=<your-app-id>

6. Review logs to see input requests and outgoing responses

After running the CLI, you can navigate to the terminal running the docker containers and view the logs, which will contain all of the calls from Fast->Seller App, as well as all of the responses from Seller App->Fast.