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So I wanted to ask, why do they need the testnet?

Same question I wanted to ask also. Will be glad if answered. Thank you!

Whats the difference?

Okay,since both of you asked the same question,i would answer it from here.

Testnets are already created platform meant to be used as a means to test out the main platform and to ensure that all the functionalities are effectively utilized and to debug the entire system making it possible for all flaws to be checked and corrected before the official launch.