One of the core features of Collected Forms is its ability to capture submissions on the existing, non-HubSpot forms on your website. For a detailed explanation of how this works, check out this article.
The HubSpot Collected Forms capture tool includes logic that allows it to intelligently identify if a form has any sensitive fields, for example a password field or a credit card field. Due to the sensitive nature of this information (and the fact that HubSpot stores form submissions in plain-text), HubSpot will not capture this information on a form.
Collected Forms achieves this check for sensitive information by scanning the form for field labels that suggest credit card information is present, such as credit card, card number, expiration, expiry, ccv, cvc, cvv, secure code, Mastercard, American Express and AMEX. In addition to this, Collected Forms will check for number fields on the form and uses a formula to identify if this number could possibly be a credit card.