How to pay for portable Wi-Fi?

Excuse me, could you please clarify how one goes about paying for portable Wi-Fi? I'm interested in the various options available and how the process typically works. Are there any upfront costs or ongoing fees that I should be aware of? Additionally, do the payment methods vary depending on the provider or location? It would be greatly appreciated if you could elaborate on the steps involved in making a payment and any potential discounts or promotions that might be available.