Activate Double Opt-In in Hubspot

For each newsletter sign-up coming from UK, you need to make sure double opt-in is activated

Signup form: is created in HubSpot Default double opt-in option from HubSpot – can only be used if the landing page is created in HubSpot, this is not the case here, so we need another solution

Action needed.

How can I activate double opt-in for everyone who signs up for this form, without moving the Landing Page to HubSpot?