For ‘End of the Month' cases, if a selected date is not present in a month (say, the 31st) for billing, then the preceding date is selected. The renewal shifts back to the original date in the subsequent month, if available.

We have migrated to new Self-Serve Calendar Billing configuration from 23 March 2023. Self-Serve Calendar Billing allows you to add multiple Site-level & Plan-level configurations also supports Yearly billing frequency. With this new configuration, you can manage both SaaS and E-Commerce business. Besides, the Advance trigger allows you to set calendar billing for specific events. Reach out to our support to enable this feature on your site.
Refer to this link on how to configure Self-Serve Calendar Billing for SaaS business
Refer to this link on how to configure Self-Serve Calendar Billing for E-Commerce business

Example:
The customer has signed up for a subscription that renews on the 31st of every month.
The renewal of the subscription will fall on Jan 31, February 28, March 31 and so on, i.e., the subscription will renew on the last day of the month.