You would be better suited going through FirstPromoter themselves and asking their own support team how to integrate it into Wix and if it is doable and Wix support it.
https://help.firstpromoter.com/en/
https://help.firstpromoter.com/en/articles/2001406-integrate-firstpromoter-with-zapier
Wix don’t provide support for third party apps and code that they have not had the chance to run and test fully on the Wix servers etc.
Also, as FirstPromoter have their own API, then I would look at using that instead through Wix Fetch.
https://docs.firstpromoter.com/#tracking-api
https://www.wix.com/corvid/reference/wix-fetch.html
https://support.wix.com/en/article/corvid-accessing-third-party-services-with-the-fetch-api