Payment is not made for how difficult it really is for the runners in SR5 (nor in SR4 before it) it is more based on the Johnson:

The expected Payment is (or should be) calculated from the value of the goals, and the difficulty *as the hirer sees it*. So Mr Johnson offers *payment according to what he knows* (as the GM, you determine that), not only what he tells the runners. 

A higher Payout than what he tells thus makes it either "urgent" for the client, or his offer is "fishy", and you do well at working with the scales. On the other hand, a low payout might coax the runners into taking a job because it makes it appear easier than it actually is. 

Examples:
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Mr. J works for Saeder-Krupp and sends the team against Novatech. He wants them to sabotage the delivery of some fish - and wants it rerouted to him. He doesn't tell them, that the fish is a genetic prototype, and that he wants to serve it to his dragon boss Lofwyr. To him, this goal is worth more than the  obvious, so he will offer something between mid to high level instead of the low to mid level that would be appropriate to how he makes it appear.

A different Mr. J works freelance. He is contracted to hire runners to sabotage an electricity station, no more info given. He doesn't know, that the triad that contracted him will use the blackout as a chance to break free some of their boys because the prison is supplied by that electricity substation. He will offer a payment based on the low level sabotage *he* thinks it is (just shut down power), not the mid level it is really (extra security as it is known to be a critical point).