Getting null project key in a Jira Cloud App sprint_started webhook

I'm developing a Jira Cloud Add on that will receive sprint related events:

"modules": {"webhooks": [      {"event": "sprint_started","url": "/sprints/started?project={project.key}&id={project.id}"      },      {"event": "sprint_closed","url": "/sprints/closed?project={project.key}&id={project.id}"      }

As described in the documentation I've used the placeholders {project.key} and {project.id} to get the information about the project in which the event was triggered.

This is the controller that is invoked:

    @PostMapping(value = ["/started", "/closed"])    fun sprintEvent(@AuthenticationPrincipal hostUser: AtlassianHostUser, @RequestParam project: String, @RequestParam id: String, @RequestBody body: Map<String, Any>): Mono<Void> {

However both project and id are null

The same thing for issue events works smoothly, receiving the project key:

"modules": {"webhooks": [      {"event": "jira:issue_created","url": "/issues/created?project={project.key}&issue={issue.key}"      },

    @PostMapping(value = ["/created", "/updated"])    fun issueEvent(@AuthenticationPrincipal hostUser: AtlassianHostUser, @RequestParam project: String, @RequestParam issue: String, @RequestBody body: Map<String, Any>): Mono<Void> {

What's the problem with the sprint events?