Activate servicehooks feature by web API

Hi All,
I’d like to setup Slack alerts on my sentry projects via web API.
I’m not using the on-premises version but the SAAS one.
When POSTing on the /{{myproject}}/hooks/ I got a 403 - [“You do not have that feature enabled”].
I understand from the documentation that I have to activate the ‘servicehooks’ feature on my project before using that call, and that this is done by modifying /src/sentry/conf/ for the on premises version of Sentry, but how do we do that for the SAAS version ?
A PUT on the project endpoint does not seem to allow that.