Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
I am sorry for the inconvenience this causes. I understand how important it is that website visitors are able to easily join your mailing list.
I would recommend that, as a user of the integration, you contact its developer directly to ask whether they plan to make the necessary updates and/or to provide feedback requesting that they do so. Per the integration's listing on the Wix App Market https://www.wix.com/app-market/constant-contact-form , they can be contacted by email at wix@digioh.zendesk.com
If it becomes necessary for you to replace the integration (or if you would prefer to replace it, regardless of whether it gets updated), there may be other compatible apps available in the Wix App Market https://www.wix.com/app-market ; although we're unable to recommend any specific app. Support for any app found in the Wix App Market would be provided by the app's developer.
Another option would be to create a sign-up form within your Constant Contact account. We offer a few types of forms:
1.) Lead Generation Landing Pages, which can be linked to a button, image, or text link on your website:
Create a Lead Generation Landing Page
https://knowledgebase.constantcontact.com/articles/KnowledgeBase/32012-Create-a-Lead-Generation-Land...
Share the URL for a Lead Generation Landing Page
https://knowledgebase.constantcontact.com/articles/KnowledgeBase/32219-Find-and-Share-the-URL-for-a-...
2.) Inline Sign-up Forms, to be embedded into a webpage:
Create an inline contact sign-up form
https://knowledgebase.constantcontact.com/articles/KnowledgeBase/18265-Create-a-Sign-Up-Form-with-th...
Once you have created and published an inline form, there are two pieces of code needed to install the form on your site. The Universal Code connects the form to your Constant Contact account, while the Inline Code identifies which form should be displayed. Both pieces of code should be added to your webpage in the same custom widget, which can be positioned on the page as desired.
Step 2 (Get the code for your sign-up form) in this article explains how to locate both pieces of code within your Constant Contact account:
Activate and install an inline sign-up form on a website
https://knowledgebase.constantcontact.com/articles/KnowledgeBase/18053-activating-and-installing-you...
The following Wix Help Center article covers adding a custom widget / HTML iFrame to a page on your site:
Wix Editor: Using iFrames to Display Visible Content on Your Site
https://support.wix.com/en/article/wix-editor-using-iframes-to-display-visible-content-on-your-site#...
3.) We do offer Pop-up Forms, however they unfortunately do not appear to be compatible with Wix websites at this time.
If you have any questions about our Inline Forms or Lead Generation Landing Pages, please contact our Customer Support team at 866-289-2101.