Is there a way for my customer to pay by Sadad in my store at ExpandCard?

Yes, there is a payment method Sadad, but it is included with the payment gateway payFort ... At the beginning you should have an account at payFort and make sure that the account is activated then you can put your account data in the payFort at your store and then activate Sadad  payment

You can open an account at the payfort via the following link :

https://www.payfort.com/en/%D9%87%D9%8A%D9%91%D8%A7-%D9%86%D8%A8%D8%AF%D8%A3/

the following photo for how to activate Sadad   payment