GoHighLevel does not use mailing lists. Instead, every opt-in is created or updated as a contact in your sub-account and given a tag. You then start your GoHighLevel workflows from that tag.
Where to find it:

Go to Free List Building → Autoresponders and find the GoHighLevel card. The card shows the same setup steps as below.
How to get your API key:
- In GoHighLevel, go to Settings → Integrations → Private Integrations.
- Click Create New Integration and name it Free List Building Website.
- Tick all four scopes: View Contacts, Edit Contacts, View Locations and View Tags. View Tags is what fills the tag dropdown.
- Copy the generated API key.
How to find your Location ID:
In GoHighLevel open Settings → Business Profile, or look in the address bar after /location/. Use the sub-account Location ID, not an agency ID.
Step by step:
- Paste the key into API Key (from Private Integration).
- Paste the ID into Location ID.
- Optional: type a Default Tag. Leave it blank to use list-builder-pro.
- Click Connect, then Test Connection.
- The card shows Default Tag with your tag and the line "All new contacts will be tagged with this value". To change it, type a new tag in Change Default Tag and click Save Tag.
- Under Default Tag (from GHL), pick one of your existing GoHighLevel tags if you prefer, then use Apply to Funnels Without a Tag or Apply to ALL Funnels.
What happens on each opt-in:
The plugin upserts the contact in your sub-account (creates it, or updates it if the email exists), with first and last name split from the name when you collect it, and adds the funnel's tag.
Per funnel tags:

On a funnel's edit page, choose GoHighLevel in Autoresponder Provider. The field below is called Tag. Pick a tag for that funnel, or leave it blank for the default.
If you change scopes later:
GoHighLevel gives you a new key when you edit the scopes of a Private Integration. Copy the new key and connect again on the card.
A real example:
Sam Rivera tags FREE Niche Selection Guide opt-ins with affiliate-niche-guide. A GoHighLevel workflow starts on that tag and sends a three day series about choosing a niche, while every other funnel uses the default tag yoursite-free-guide.
Tips:
- Use clear tag names that match the funnel, like ai-prompts or webinar-signup.
- Tags are kept for 24 hours; click Refresh Tags after creating new ones.
- The Debug Log in Settings explains GoHighLevel replies in plain words, for example when a scope is missing.