Hi @lm97 I think that the problem here is that x and y are inverted. For the record, the code below works as intended
import plotly.express as px
import plotly.graph_objects as go
import pandas as pd
df = px.data.iris()
mat = pd.crosstab(df['petal_width'], df['sepal_width'])
fig = go.Figure(go.Heatmap(x=mat.columns, y=mat.index, z=mat))
fig.show()
