plt.figure(figsize=(12,7))
sns.relplot(kind='line',data=merge_wrp,x='month_name',y='Amount_tran',hue='Product',
errorbar=None,row_order=['April','May','June','July', 'August','September',
'October','November','December','January', 'February','March'])
plt.xticks(rotation=50)
plt.show()

row_orderandcol_orderdon't refer to thex-or-y axisof one plot. It make sense if you usecolandrowparameters to draw more than one chart. In your case, you have to sort your dataframe first. It can be done withpd.CategoricalDType: