Hi

I am using Datastream Web Service in Python and try to retrieve a time series of daily price changes (expression) for a single instrument or multiple instruments over a certain time horizon.

df=ds.get_data(tickers='S:NESN', fields='PCH#(X,1D)', start='-2Y', end='-0D', freq='W')

If I run this request, I receive the following error message:

Error - please check instruments and parameters (time series or static)

What am I doing wrong?

Thanks for your help.