Hi there @ChiaraC,
I did a quick check on our integrations, and it looks like Treatwell hasn't built an integration with us yet.
Most new Zapier integrations are built by the company or team that created the app, so I'd recommend you also encourage their team to add their app to Zapier via our developer platform: https://zapier.com/platform
Nevertheless, I've added your vote to our internal app wishlist, and we'll be sure to let you know if/when this app is added to Zapier.
In case you're curious, here's more on how new services typically get added to Zapier: https://zapier.com/help/manage/app-connections/request-to-add-a-new-app-to-zapier
In the meantime, if Treatwell supports webhooks. You might be able to integrate them using our Webhooks by Zapier app. Please note that Webhooks by Zapier is considered as an advanced feature and requires knowledge about APIs. If you need help setting up a Webhooks connection. I suggest reaching out to our directory of Zapier Experts here: https://zapier.com/experts
Hopefully, this helps! 😊