As per the official documentation it lies inside chat room option. But its not available there.
2 Answers
Enable Webhook, option can only be visible if you have google workspace account. It's not available on personnel gmail account.
The Configure webhook option is indeed available only for Workspace users so you will have to use a Workspace account in order to set it up.
As for the documentation, I have taken the opportunity to file this report in order to improve the documentation regarding this.
I suggest you star it as all the updates will be posted there.
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