HTTP Error 400: Bad Request - Need Help

I am trying to store a Data Table into a pandas dataframe within my personal (Uplink) server-side code, and then apply some logic to it. When I execute the code in my IDE, it works fine. But when I initiate it via function that is called from clicking a button on the Client Side, it gives me an HTTP Error 400.

Note: I am using a free version

Below is my code snippet:

SERVER CODE (Used in my Spyder IDE)
@anvil.server.callable
def test():
df_fr = pd.read_csv(app_tables.forecast_rev.search().to_csv().url)

CLIENT CODE
def button_test_click(self, **event_args):
“”“This method is called when the button is clicked”""
anvil.server.call(‘test’)