After I edit the entries in the new tagify extension, it appears to send through an array, the first element is a string containing all of the tags, followed by each of the individual tags as individual elements.
Can you check how the Form Data (Payload) looks like. The post data should only contain the individual elements and not the concatenated string you have as first item.
Depending on what project type you have it can differ.
With NodeJS project it is in public/dmxAppConnect/dmxTagify, with most other projects it is dmxAppConnect/dmxTagify. With mobile (cordova) project it is located in www/dmxAppConnect/dmxTagify.
Could you please show how your payload looks like, the data send to the server before it is being processed on the server, you see it in the payload tab.