Short answer
HubSpot's KB: live validation is on by default, using each property's rules.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Visitors must meet the property's rules before they can submit.
On by default.
HubSpot's KB: live validation is on by default, using each property's rules.
The relevant screen in my demo portal.

Visitors must meet the property's rules before they can submit.
One email when a new article publishes.
If this did not fix it, the problem is probably specific to your setup. Book a call and we will look at it together.
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