Event Grid sys topic synchronous subscription validation

I'm facing a stange behavior where subscritpion creation is not waiting for the webhook response where I return back the validation code. As a workaround i'm calling the url validation to validate the provisionning of my subscription.

Steps to reproduce :

PUT Call to :

https://management.azure.com/subscriptions/{sub_id}/resourceGroups/{myrg}/providers/Microsoft.EventGrid/systemTopics/{my-sys-topic}/eventSubscriptions/{sub-name}?api-version=2022-06-15

the API response return an "Updating" or "Creationg" in provisionningstate but my webhook return the validation code :

{
"validationResponse": "the validation code received from the event"
}

I usually use this sync validation and never faced any issue until this new project.

Start by reproducing the PUT request against the Event Grid system topic event-subscription endpoint using the supplied API version and webhook validation response. Compare the subscription provisioning state with the webhook response and document whether synchronous validation is expected to complete creation; the issue is done when the behavior and required resolution are established.

Written by the indexing model from the issue text.