I am a regular user of Plotly with python, but only on my own computer, where I don't run more than a couple of instances of plotly at the same time. However, I now need to run several copies of my program, which uses plotly, simultaneously on a remote server. I use the following lines at the top of my code:

import plotly.plotly as py
py.sign_in('id','key') ## necessary for server simulations
This has worked for me all along, but I now get the error message:

plotly.exceptions.PlotlyError: Sign in failed.

So, what is going on? Do I need to pay even for offline use of Plotly?