How to make the side reactions (SEI, Li plating, etc) in the interface dependent of stoichiometry

[Brushnie33]

It is straightforward to change a parameter from pybamm.Parameter to pybamm.FunctionParameter, but the challenge is to specify the sto parameter in the side reactions in the interface folder, for instance, if I would like to make the "SEI kinetic rate constant [m.s-1]" to be dependent of sto, I could define it in the class of ParticleLithiumIonParameters(BaseParameters):

def k_sei(self, sto):

    domain, Domain = self.domain_Domain
    inputs = {
        f"{Domain} particle stoichiometry": sto,
    }
    return pybamm.FunctionParameter(
        f"{self.phase_prefactor}SEI kinetic rate constant [m.s-1]",
        inputs,
    )

And in the sei_growth.py codes, if I add the following codes:
sto = variables[f"{Domain} particle concentration"]
And change phase_param.k_sei to phase_param.k_sei(sto) in the following equation:
k_exp = phase_param.k_sei(sto) * pybamm.exp(-alpha_SEI * F_RT * eta_SEI)

And in the parameter file, I added the function:

And change the value for the k_sei:
"SEI kinetic rate constant [m.s-1]": k_sei_function, # 1e-12,

I got errors: