The acf plot exponentially decays after a lag spike at 2 and the pacf plot cuts off after lag 0. So, this indicates that the time series is stationary. But after doing adf.test and Kpss test, the result tells difference story.
Augmented Dickey-Fuller Test data: ltc.ts Dickey-Fuller = 1.7982, Lag order = 3, p-value = 0.99 alternative hypothesis: stationary
P-value of adf.test is 0.99 and I can not reject the null hypothesis : non-stationary
KPSS Test for Level Stationarity data: ltc.ts KPSS Level = 0.53558, Truncation lag parameter = 1, p-value = 0.03365
P-value of KPSS test is 0.03 and I cant reject the null hypothesis : stationary.
What would I should do in this case? Should I follow the graph or test result. Please give me an advice!