How to top up on Lydia?

Excuse me, could you kindly elaborate on the process of topping up on Lydia? I'm a bit unclear on the steps involved. Are there specific methods or channels that I should be aware of? Is it a straightforward procedure, or does it require some form of verification or authorization? Additionally, are there any fees associated with topping up my Lydia account? I'd greatly appreciate it if you could guide me through the entire process, step-by-step. Thank you in advance for your assistance.