Does the trial ask for a credit card?

No — the signup form takes no card details at all, on either plan track. What differs is what happens next. On a monthly plan you get the 15-day trial and the page simply pauses at day 15 if you have not subscribed; nothing charges itself. Pay-as-you-go has no trial, because there is no monthly fee to try — you sign up the same way, then add a card from Settings → Plan & billing, and the plan only switches on once that card is saved. Until then no plan is active and nothing can be charged.