Open a fresh session and cut-and-paste the reprex](https://community.rstudiocom/t/faq-how-to-do-a-minimal-reproducible-example-reprx-for-beginners/23061). If you still have problems, post a revised reprex.
suppressPackageStartupMessages({
library(forecast)
})
input <- c(467.38,441.67,579.30,600.41,793.38,576.80,741.21,634.66,582.00,661.35,249.46,482.33,516.02,241.41,443.20,502.98,497.31,668.08,596.89,686.76,598.28,598.23,391.71,492.66,325.89,253.30,737.37,462.75,609.31,559.05,581.16,680.36,753.18,476.41,3.12,608.01,428.74,584.53,508.92,655.63,867.83,1059.98,509.34,820.85,825.13)
newdata <- ts(input, start = c(2015,1), frequency = 12)
fitARIMA <- arima(newdata, order=c(0,0,0),seasonal = list(order = c(1,0,0), period = 12))
summary(fitARIMA)
#>
#> Call:
#> arima(x = newdata, order = c(0, 0, 0), seasonal = list(order = c(1, 0, 0), period = 12))
#>
#> Coefficients:
#> sar1 intercept
#> 0.4770 572.1038
#> s.e. 0.1608 38.5140
#>
#> sigma^2 estimated as 26880: log likelihood = -294.88, aic = 595.76
#>
#> Training set error measures:
#> ME RMSE MAE MPE MAPE MASE ACF1
#> Training set 0.7347081 163.9509 121.5846 -349.8801 365.849 0.711663 0.1364518