Do you have to pay to go in. ?

Yes.

You can pay by a cash or credit cards in front of main gate.

Admission is FREE for all Members, School Groups, and San Francisco City & County Residents (with proof of residency). Non-resident Admission is $9 for adults with discounts for seniors, youth, and families. Full details including Free Day information can be found here: https://www.sfbg.org/visit

Also free entry before 9am for all

It's free entry if you're a resident of San Francisco. For everyone else, there is an entry fee of $8/adult.