error in forecast using Arima with exogenous variable.

Hi. i am having this issue when using forecast function with Arima and exogenous variables.However, predict function gives some results.

No regressors provided
in addition:Warning message:
The non-existent newxreg arguments will be ignored

i am trying to forecast 12 years ahead "loss" considering the exogenous variable "har". Here is the attempt.

harw<- cbind(
ArLag0 = har,
ArLag1 = stats::lag(har,-1))%>%
exvector is the future values of the exogenous variable which has been forecasted separetely.
exvector=ts(har[c(54:65),]$value,start = min(har[c(54:65),]$year),frequency=1)
newdat=cbind(ArLag0=exvector, ArLag1=y)


Referred here by Forecasting: Principles and Practice, by Rob J Hyndman and George Athanasopoulos