Sphere of Safety-what if your opponent has to attack?

[Agrus Kos, Enforcer of Truth]

If I have {Sphere of Safety} out (can't be attacked unless they pay x where x is the amount of enchantments you control) and on of their creatures has {Furor of the Bitten} does it still attack ignoring the sphere, only attack if they can pay or are they somehow forced to pay and penalized if they don't?

[Kaleo42]

In these cases they may choose not to pay and therefore give up the actual ability to attack.

[Keyeto]

The opponent can choose not to attack. From the Sphere's ruling on Gatherer:

10/1/2012 If you control Sphere of Safety, your opponents can choose not to attack with a creature with an ability that says it attacks if able.

[Agrus Kos, Enforcer of Truth]

Thanks