How does PayPal actually process a transaction when a customer submits a payment?

There are a couple of scenarios:

• If both the Payer & Payee are PayPal customers, the transaction is internal to PayPal's ecosystem and hence it is just an intra-adjustment funds within PayPal's accounting.
• If a Customer pays to a PayPal user using their own Credit Card or Debit Card, then PayPal is acting as the payment processor for the card transaction and then crediting the amount into PayPal user's account.
• If a PayPal customer wants to charge their PayPal Debit Card, then it is a straight forward Card transaction, provided the PayPal account has the money to cover the transaction.
• If a PayPal customer wants to load funds into their PayPal Account from their own bank, this is nothing more than an ACH transfer into PayPal.
• The same is true for reverse, when you want to withdraw into your bank account, this again is an ACH transfer from PayPal's bank into your own bank account.

To get a better understanding of How/What PayPal is - you can read this descriptive answer that answers visually what PayPal is: 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 ☏?