I need to find exact and numerical solutions to a function but my code in R shows Error in optim(start_val[i, ], g) :
function cannot be evaluated at initial parameters

that is my code:
g <- function(x) (3x[1]+2x[2]+4x[3]-4)^2 + (4x[1]+2x[2]+4x[3]-2)^2 + (1x[1]+1x[2]+4*x[3]-4)^2

start_val <- expand.grid(c(-10,0,10),c(-10,0,10),c(-10,0,10))

optim_on_a_multiple_grid <-

function(start_val, fun, …) {

opt_result <- sapply(1:nrow(start_val),
                     
                     function(i) {
                       
                       res <- optim(start_val[i,], g)
                       
                       c(res[[1]], res[[2]], res[[4]])
                       
                     })

rownames(opt_result) <-
  
  c(paste("x_", 1:ncol(start_val),
          
          "_start_val", sep = ""),
    
    paste("x_", 1:ncol(start_val),
          
          "_sol", sep = ""),
    
    paste(c(deparse(substitute(
      
      fun
      
    )), "_min"), collapse = ""),
    
    "convergence")

opt_result

}

round(optim_on_a_multiple_grid(expand.grid(c(-10, 0, 10), c(-10, 0, 10)), g), 3)

Please, point me at my mistakes and explain how to fix them, I am stuck on it for quite a while now