Problems inserting custom code before </body>?

https://support.wix.com/en/article/embedding-custom-code-to-your-site
https://support.wix.com/en/article/about-tracking-tools-analytics

This is not a code related issue and therefore you should be going through Wix Support for more help with this
https://support.wix.com/en/article/contacting-wix-customer-care-for-support

Also, please note that with any custom code used, that Wix will not provide support.
Wix does not provide support for technical difficulties associated with third-party code snippets. If you are experiencing an issue with your code snippet, please contact the provider directly.