The four major ways to change Monthly Recurring Revenue (MRR) are through new subscriptions, expansions, contractions and churn.
This occurs when a new or existing customer starts a new active subscription or upgrades from a free subscription to a paid subscription.
This occurs when an existing paid subscription is upgraded or modified to increase its MRR. This can happen by adding or changing a plan, increasing the quantity or lowering a discount.
This occurs when an existing paid subscription is downgraded or modified to decrease its MRR (to a non-zero amount). This can happen by removing or changing a plan, lowering the quantity or increasing a discount.
This occurs when an existing paid subscription is either cancelled, downgraded to a free subscription or becomes delinquent. Note that when the trial ends on a new subscription for a customer without a saved payment method, the subscription briefly moves from status=trialling to status=active before the first invoice fails payment and the subscription becomes status=past_due.
For recommendations on how to use Billing to increase your MRR, see Ways to grow your monthly recurring revenue (MRR).