CallBack Error updating graph.figure - DASH - callback

Question

New here and to the world of python.
Generating a histogram plot where it changes color when a postcode is selected.
Now I have the main histogram but when the postcode is selected from the dropdown it gives the error. Unable to figure out how to resolve this. I have provided my full code below.
Let me know if more info is required to figure out the error. Something to do with input
import pandas as pd
import plotly.express as px
from dash import Dash, html, dcc, Input, Output
app = Dash(__name__)
app.title = "EGMs in NSW"
# Load your data : br = .....
datalist=pd.read_excel('premises-list-Aug-2022.xlsx',skiprows=[0,1,2])
datalist['Licence type'] = datalist['Licence type'].str.split(" - ").str.get(1)
datalist['Licence type'] = datalist['Licence type'].str.title()
postcode = datalist['Postcode']
postcode = postcode.sort_values(ascending=True)
postcode=list(dict.fromkeys(postcode))
pd.Series(datalist['Postcode'].unique()).sort_values(ascending=True)
def make_histogram_plot():
# Create scatter plot
fig=px.histogram(
data_frame = datalist,
x='Licence type',y='EGMs',color='Postcode',title='EGMs by Licence Type in NSW',
histfunc='avg'
)
fig.update_traces(marker=dict(color="#002664"))
fig.update_layout(
plot_bgcolor='#EAEDF4',
xaxis_title=None,
yaxis_title='Average EGMs'
)
return fig
app.layout = html.Div(children=[
html.Div([
dcc.Dropdown(postcode,value=[], placeholder="Select postcodes", multi=True, id='postcodes')
]),
dcc.Graph(id = 'graph',figure = make_histogram_plot())
])
#app.callback(
Output('graph','figure'),
Input('postcodes','value')
)
def dropdown_changed(postcodes):
if postcodes==[]:
fig = make_histogram_plot()
else:
datalist2 = datalist[datalist['Postcode'].isin(postcodes)],
# Create scatter plot
fig=px.histogram(
data_frame = datalist2,
x='Licence type',y='EGMs',color='Postcode',title='EGMs by Licence Type in NSW',
histfunc='avg'
)
fig.update_traces(marker=dict(color="#002664"))
fig.update_layout(
plot_bgcolor='#EAEDF4',
xaxis_title=None,
yaxis_title='Average EGMs'
)
return fig
# Start the server
if __name__ == '__main__':
app.run_server(debug=True)