Payment authorization on modern money transfer systems like Paypal, venmo

Authorization

Clearing / netting

if 100 people are sendind money to each other, clearing means to figure out minimum number of transactions to settle every one.

Person A sends money, but receives money from some one else. Instead of making transactions on each and every money operation, clearing/netting calculates the input and output for each person.

settlement

the final amendment of the record.

Chaning the balance from 10 to 11.

Modern Payment Systems

PSPs = payment service provider

Stripe, First Data, Adyen they are PSPs

Merchant doesn't want to deal with Visa, mastercard etc. they deal with PSP's and PSPs will deal with visa and mastercard and other banks on merchants behalf

Correspondence Banking

I am small bank in US and i need to send money to Pakistan.

But Pakistan doesn't recognize me due to lack of trust so i need help of a bigger bank whom Pakistan recognizes. That big bank is correspondent bank to me.

Ripple tries to be a bridge between banks making a transfer with each other

Fiat → XRP → Fiat

Ripple started off as a competitor to SWIFT

I have still not understood double spending problem