Difference between external Registration URL Link - Prospective Vs Spend Authorized

Content

I would like to know what is the key difference between prospective and spend authorized link URL's. I see that both are having similar feilds and there is no difference where the supplier can indicate if they are registering for spend authorized or prospective? How is this behaviour controlled when customers publish these links to the suppliers in thier external website.

Any explanation on the difference between the spend authorized and prospective registration URL links will be helpfull.