I'm trying to animate a horizontal line moving down

Question

The 2D array I'm using to plot a horizontal line seems fine - range of x-values, y-values are all ones - but when I plot it through a class and FuncAnimation it is a stationary diagonal line across the plot.

I've tried transposing the array, and getting rid of the variable and just hard coding the data directly into set_data([],[]). I've altered my code slightly numerous times but I don't know what's causing the plot to do this.

lineX = np.linspace(0, 1, n)
lineY = np.ones(n)
lid = np.array((lineX, lineY))

simulation = practiceSim(pos, vel, r, m, lid)

fig = plt.figure(figsize = (10,5), dpi = 100)
fig.subplots_adjust(left=0, right=0.97)
simulation_ax = fig.add_subplot(111, aspect='equal', autoscale_on = False)

particles, = simulation_ax.plot([], [], 'ko')
line, = simulation_ax.plot([], [], 'b')

def init_anim():
    particles.set_data([],[])
    line.set_data([],[])
    return particles, line

def animate(i):
    global simulation
    simulation.advance(dt)#, lineVel)
        
    particles.set_data(simulation.pos[:,0], simulation.pos[:,1])
    particles.set_markersize(0.5)
    
    simulation.rad *= i
    simulation.lid[:,0] -= simulation.rad

    line.set_data(simulation.lid[:,0], simulation.lid[:,1])
    line.set_markersize(2)
    
    return particles, line

N = 1000
anim = FuncAnimation(fig, animate, frames = N, interval=10, blit=False,
                     init_func = init_anim)

plt.show()