How does a payment system like PayPal function end to end?

I wrote an answer that pretty much is what you're looking for: Faisal Khan's answer to What is a Paypal account? Is it a kind of bank account which is maintained for demand deposits? __ 𝐏𝐥𝐞𝐚𝐬𝐞 𝐂𝐚𝐥𝐥 PayPal 𝐓𝐨𝐥𝐥 𝐅𝐫𝐞𝐞 𝐒𝐮𝐩𝐩𝐨𝐫𝐭 𝐍𝐮𝐦𝐛𝐞𝐫 ☏+❶►❽❺❻▁❹❼❺►❷❺❺❺ ☏?