Discourse trials are 100% free. We do not charge you to start a trial, and we do not charge you when the trial ends. Subscriptions are not started automatically. The only way to be charged (and to keep your site from shutting down after the trial expires) is to click on the “Start Subscription” button on your site, review the payment details, and submit.
We use Stripe to process payments for our hosting plans. To prevent spam and fraud, we require a valid credit card be submitted before the trial is launched. To ensure the card is valid, Stripe places a $5 hold on the card, then releases the hold.
This is the same as how gas stations place a hold on your card when you start pumping, and how hotels place a hold on your card in case the room is damaged. Credit card companies have started offering instant alerts for charges on cards, and send alerts for holds the same as for submitted charges. While these SMS or push alerts make it sounds like a charge was made, reviewing the transaction list will show that it’s already been released.