What are the difference between "Upon" and "After"

[Kumarc]

1. Upon receiving payment, the seller will dispatch the goods to the buyer.
2. After receiving payment, the seller will dispatch the goods to the buyer.

What are the difference between "Upon" and "After" in the context?

 

[tedmc]

What is the difference...
Both mean the same; the second action follows from the first.

 

[PeterCW]

What is the difference...
Both mean the same; the second action follows from the first.

Not quite. "Upon" means that the second action must follow immediately. "After" means that the second action may follow at some point in the future.