SARIMAX prediction DECAYS to ZERO for future data and does not print correspinding futures dates!

[ZEVtheNukeGuy]

Howdy folks, I'm new to python and trying to forecast a time series of total sales from a store using SARIMAX. The data spans over 5-years (daily) from '2013-01-01' to '2017-08-16' . I wish to predict sales for the next 30 days ( i.e. from '2017-08-17' to '2017-09-15').

Here is the sample data, read usingthis piece of code
import pandas as pd
import numpy as np
from statsmodels.tsa.statespace.sarimax import SARIMAX
import pmdarima as pmd

DF_store = pd.read_csv('Per_store_DF', index_col = "date", parse_dates = True)
DF_store

I decided to split the data into Train and Test sets - 80/20, Then use the pmdarima function to guess the optimal ARIMA model order, then train the model with SARIMAX on my endogenous data.
N = round((80/100)*len(DF_store))
DF_train = DF_store.iloc[:N]
DF_test = DF_store.iloc[N:]
DF_train

Model Function

def arima_generator(ts):
auto_model = pmd.auto_arima(ts, start_p = 1, start_q = 1, max_p = 3, max_q = 3, m = 30, test = "adf", trace = True)
return auto_model

Apply the model function

ARIMA_model = arima_generator(DF_train)
ARIMA_model.summary()

Porblems arise when I train the resulting model on my Training set and try to predict the Test data.
model = SARIMAX(DF_train, order =(1,0,0), seas_order = (0,0,0, 30))
result = model.fit()
result.summary()

start = len(DF_train)
end = len(DF_store)

Using

predict = result.predict(start, end, dynamic = False)' (same with True) DF_train.plot(legend = True, figsize=(15,10)) predict.plot(legend = True) predict`

1. The outpust has no dates
2. It decays to zero as shown in these pictures.
   

Using "start = len(DF_test)" Only

start = len(DF_test)
predict = result.predict(start, dynamic = False)' (same with True)

Starting Somewhere along the Train dataset

It predicts to the end of the set but then decays to zero for future values as shown
start = len(DF_test)
end = len(DF_train)+ len(DF_test)-1
predict = result.predict(start, end, dynamic = False)

#Questions.
Summary is mymodel will NOT work for any future dates.

• why is this happening?
• Is there anything i'm missing?
  I'll be gald if someone could help.
  Thanksin advance.
  This is the dataset: Per_store_DF.csv