How to fix “'The `start` argument could not be matched to a location related to the index of the data.” Error?

Question

When I try to predict the results using ARIMA for a specific train/test split, its throwing an error like this:

"'The start argument could not be matched to a location related to the index of the data"

This the code i have been trying: pred0 = results.get_prediction( start = '2019-06-20', dynamic=False)

Same happens for get_forecast() method.