App Instance Installed webhook - recommended pattern to bind a new install to an external user account?

Hi community,

I’m building a third-party backend that integrates with merchants’ Wix stores. The integration imports orders from Wix into our accounting system. I have a Custom App and I’m using the modern OAuth flow (grant_type=client_credentials + instance_id), since per the docs custom authentication (refresh_token flow) is no longer available for new apps.

I’ve thoroughly reviewed the docs and the community forum and can’t find an answer to a specific design question. Before posting in the forum, I’d like to confirm directly with you.

The scenario

A user logged into my app clicks “Connect my Wix store”. We want, by the end of the install flow, to have an instance_id persisted in our database bound to the correct user account (e.g. account_id=42). All subsequent
API calls then use client_credentials + instance_id and run for that account.

What I’ve confirmed from the docs

  • App Instance Installed webhook payload schema contains only two fields: appId and originInstanceId. There’s no state, token,
    metadata, or custom field allowing the install initiator to pass arbitrary context through.
  • The deprecated /installer/install?appId=…&redirectUrl=…&token=… flow (custom authentication) used to allow this via the token parameter, but per the docs it’s no longer available for new apps.
  • The Redirect URL configured in the dev portal is app-level (single value), not per-install, it can’t carry per-user state by itself.
  • “Share install link” generates a single shared link without a per-recipient state parameter (or at least none documented).

What I’ve searched on the forum

I went through the forum and the closest threads are:

None directly answer the question.

My concrete questions

  1. Is there an officially supported mechanism for an external SaaS to bind a new install to a known external user account at install time? If yes, where is it documented?
  2. Can the Share Install Link be parameterised per recipient (so each user gets a unique link encoding their account id) — and if so, does Wix echo that parameter back in any webhook payload?
  3. If neither is possible, what is Wix’s recommended pattern for this use case?

Thanks!

Got a response from the Wix support, this page explains how to use “postInstallationUrl” that will be send to the app after the install completes: https://dev.wix.com/docs/build-apps/launch-your-app/app-distribution/install-your-app/about-the-external-install-flow