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Choropleth map is not getting generated from mapboxmap

I am able to generate the choropleth map using go.Choroplethmapbox in jupyter notebook. But when I try this in dash app, I am getting nothin. I am updating graph through call back. Please help me to get the choropleth map. Call back code is given below:

@app.callback(
    Output('example-graph', 'figure'),
    [Input('zoom','value')])
def update_fig(z_value):        

    fig = go.Figure([go.Choroplethmapbox(geojson=j_file, locations=df.area_code, z=df.total_count,

                                    colorscale="Viridis", zmin=0, zmax=150,

                                    marker_opacity=0.5, marker_line_width=0)])        

    fig.update_layout(mapbox_style="basic",

                        mapbox_accesstoken=mapbox_access_token,

                        mapbox_zoom=z_value, mapbox_center = {"lat":52.480271148513935, "lon":-1.90887451171875})

    #fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})    
    
    return fig

I encountered the same problem, figure is generated correctly just somehow not displayed in a dcc.Graph object.