Gravity Forms Listmonk Connector

Minimal Gravity Forms feed add-on that pushes form submissions into Listmonk using its REST API.

This plugin is intended for site owners who already use Gravity Forms and Listmonk and want a simple, reliable way to add or update subscribers when a form is submitted.

Features

• Listmonk API integration using basic authentication
• Per-form feeds via the Gravity Forms Add-On framework
• Field mapping for email and name
• Static list presets (multi-select from Listmonk lists)
• Dynamic list assignment based on submitted field values (IDs via text/select/checkbox/JSON)
• Subscriber attributes through a JSON field with merge-tag support
• Retry support from the Gravity Forms entry detail screen
• Translatable (text domain eightam-gf-listmonk, German de_DE included)

Requirements

• WordPress 5.8+
• PHP 7.4+
• Gravity Forms 2.5+
• A running Listmonk instance with API access over HTTPS

Installation

1. Install and activate Gravity Forms.
2. Copy this plugin into wp-content/plugins/eightam-gravity-listmonk or install it as a normal WordPress plugin.
3. Activate Gravity Forms Listmonk Connector in Plugins → Installed Plugins.

If Gravity Forms is not active, the add-on will not register and no feeds will run.

Configuration

1. Global Listmonk settings

1. Go to Forms → Settings → Listmonk.
2. Enter your Base URL, e.g. https://listmonk.example.com/.
3. Enter the API Username and API Key / Token.
4. Optionally enable Preconfirm Subscriptions by Default if you want to skip double opt-in globally.

These settings are used for all feeds unless overridden per feed.

2. Creating a feed for a form

1. Open Forms → Forms, edit a form, and go to Settings → Listmonk.
2. Click Add New to create a feed.
3. Configure:
   • Feed Name: Any label to identify this feed.
   • Field Mapping:
     • Email Address (required)
     • Name (optional)
   • Attributes JSON (optional): a JSON object of custom attributes.
     • Example: { "city": "Berlin", "source": "website" }
     • Merge tags are supported and are replaced before sending to Listmonk.

3. List assignment

You can assign subscribers to lists in two ways (they can be combined):

• List Presets (Optional)

  • Multi-select of Listmonk lists fetched from the API.
  • Selected lists are always applied to the subscriber.

• Dynamic List Field

  • Choose a form field whose submitted value(s) resolve to Listmonk list IDs.
  • Supported patterns:
    • Comma-separated list IDs, e.g. 1,2,3
    • JSON array of IDs, e.g. [1, 2, 3]
    • Checkbox/select fields whose choice values are list IDs

4. Preconfirm mode

Per feed you can control whether subscriptions are preconfirmed:

• Inherit global setting (default)
• Always preconfirm this feed
• Require confirmation (double opt-in)

The resulting boolean is sent as preconfirm_subscriptions to Listmonk.

How it works

On successful form submission, the feed:

1. Resolves the mapped email and name.
2. Resolves list IDs from presets and the dynamic field.
3. Builds an attributes payload from the JSON field after merge-tag replacement.
4. Calls the Listmonk API to create a subscriber.
5. On HTTP 409 (already exists), looks up the subscriber by email and merges the new data with existing data:
   • Lists: Combines existing and new lists (no duplicates)
   • Attributes: New values override old values, but existing attributes not in the new submission are preserved
   • Name: Keeps existing name if new name is empty
   • Status: Preserves existing status unless explicitly changed
6. Writes a note to the Gravity Forms entry with success or error details.

Retrying a sync

On the Entry detail screen for a form with a Listmonk feed:

1. Open the entry in the admin.
2. Use the Listmonk Actions meta box.
3. Click Retry Feed.

All active Listmonk feeds for that form will be re-run for the selected entry.

Permissions: only users with the gravityforms_listmonk capability can see and use this box.

Translations

• Text domain: eightam-gf-listmonk
• Domain path: /languages
• Included: de_DE translation (languages/eightam-gf-listmonk-de_DE.po)

To adjust translations or generate a .mo file, open the .po file in a tool like Poedit and save/compile it. When deployed via WordPress.org, translations are typically managed via GlotPress instead.