Evaluate the value of polyvars in SOSModel

Hi, I have a question about how to evaluate the values of polyvars in SOSModel. In the following example, there is only one regular JuMP decision variable γ and γ can be evaluated by value(γ). But when I want to check the values of x1 and x2, value(x1) does not work. How should I check the current value of polyvar x1 and x2? Thanks for your help in advance!

using SumOfSquares
using DynamicPolynomials
using MosekTools

# Create symbolic variables (not JuMP decision variables)
@polyvar x1 x2

# Create a Sum of Squares JuMP model with the Mosek solver
model = SOSModel(with_optimizer(Mosek.Optimizer))

# Create a JuMP decision variable for the lower bound
@variable(model, γ)

# f(x) is the Goldstein-Price function
f1 = x1+x2+1
f2 = 19-14*x1+3*x1^2-14*x2+6*x1*x2+3*x2^2
f3 = 2*x1-3*x2
f4 = 18-32*x1+12*x1^2+48*x2-36*x1*x2+27*x2^2

f = (1+f1^2*f2)*(30+f3^2*f4)

# Constraints f(x) - γ to be sum of squares
@constraint(model, f >= γ)

@objective(model, Max, γ)


# The lower bound found is 3