Colouring a surface using Mesh3d in python plotly

Question

I would aim to colour a surface in a 3D plot, created using plotly.graph_objects.

I worked on an approach incorporating Mesh3d, the code runs, but the wanted surface is still not coloured. What is the mistake I made, or should another approach be used?

The final outcome is desired to look similar to this 3D plot:

And this is where I am at now (I don't aim to apply color scaling to the surface, it is good enough to be filled with a consistent colour):

So, the aim would be to colour the surface where the vertical lines are connecting the two curves (2D and the same in 3D).

Here is my code:

import plotly.graph_objects as go
import numpy as np

def plot_3d_course_profile(x, y, z, color_attribute, colorbar_label):
    fig = go.Figure()

    # Bottom curve at altitude = 350
    fig.add_trace(go.Scatter3d(
        x=x,
        y=y,
        z=[350] * len(x),
        mode='lines',
        line=dict(
            color='black',
            width=5,
        )
    ))

    # Profile curve
    fig.add_trace(go.Scatter3d(
        x=x,
        y=y,
        z=z,
        mode='lines',
        line=dict(
            color=color_attribute,
            width=13,
            colorscale='Jet',
            colorbar=dict(
                title=dict(
                    text=colorbar_label,
                    font=dict(size=14, color='black')
                ),
                thickness=20,
                len=0.6,
                tickfont=dict(size=12, color='black'),
                tickmode='linear',
                tickformat='.2f',
                outlinewidth=1,
                outlinecolor='black'
            )
        )
    ))

    # Vertical lines
    for i in range(0, len(x), 7):
        xi, yi, zi = x[i], y[i], z[i]
        fig.add_trace(go.Scatter3d(
            x=[xi, xi],
            y=[yi, yi],
            z=[350, zi],
            mode='lines',
            line=dict(color='dimgray', width=4),
            opacity=0.6,
            showlegend=False
        ))

        # surface - not displaying
    fig.add_trace(go.Mesh3d(
        x=np.concatenate([x, x[::-1]]),  
        y=np.concatenate([y, y[::-1]]),
        z=np.concatenate([[350] * len(x), z[::-1]]),
        color='blue',
        opacity=0.5,
        showscale=False
    ))
        
    fig.update_layout(
        template='plotly_white',
        scene=dict(
            xaxis=dict(title='Meters north from start position', showgrid=True, gridcolor='lightblue', zeroline=False),
            yaxis=dict(title='Meters east from start position', showgrid=True, gridcolor='lightblue', zeroline=False),
            zaxis=dict(title='Altitude [m]', showgrid=True, gridcolor='lightblue', zeroline=False),
            aspectmode='manual',
            aspectratio=dict(x=1.25, y=1, z=0.7)
        ),
        title=f'3D Course Profile Colored by {colorbar_label}',
        margin=dict(l=0, r=0, b=0, t=50)
    )

    fig.show()