How do I renew a customer without resetting their login?

Always use renew (or extend) on the customer's existing line in your panel. Don't create a new line:

• Renewing adds the new time on top of the current end date.
• The customer's username and password stay the same, so nothing changes in their app.
• A new line would give them a new login, and they would have to set up every device again.

Renew before the end date so your customer has no gap. The panel deducts the credits for the renewal length.