“Test mode” for Stripe payments disables fields in preview

Hi,

Am testing the Stripe (non-recurring) payments via various forms.

Tried to check if the forms were working properly, and activated “Test mode” in Settings / Payments. [reference https://wpforms.com/docs/how-to-test-stripe-payments-on-your-site/ ]

Previewing a form (form preview option in WPForms), I get a message “Credit Card field is disabled, Stripe keys are missing.”

Without this field, how am I supposed to test, even with fake credit card numbers provided by Stripe?

SIncerely
DJM