First, you need to copy your tracking code for your specific campaign (here's how)
Step 2 - Open your Wix site Dashboard
Go to Settings in your site's dashboard.
Click the Custom Code tab in the Advanced section.
Click + Add Custom Code at the top right.
Paste the code snippet in the text box.
Enter a name for your code.
Tip:Give it a name that is easy to recognize so you can quickly identify it later (e.g Modal-forms)
Select an option under Add Code to Pages:
All pages: This adds the code to all of your site's pages, including any new pages that you create in the future. Choose whether to load the code only once per visit, or on each page your visitor opens.
Choose specific pages: Use the drop-down menu to select the relevant pages.
You will get to choose where to place your code under Place Code in:
Choose "Head"