Why paystub needed in H1 transfer?

Question

I want to transfer from Company 'A' to Company 'B'. I understand H1 transfer requires a recent copy of paystub. Why is it needed? For verification of employement or verification of income? When sending requirements to Company 'B' can I say that I am making more money if I am underpaid with Company 'A' and when they transfer H1 with a paystub attached, would that be an issue, because paystub will actually show that I get paid less?
Thanks in advance for answers.

Answer 1

The paystub proves both employment AND income. That's why they want to see it.