Error in model.frame.default : invalid type (S4) for variable

[smokarran]

Hello, I am new to RStudio software. I'm trying to use an SVM function with "terra", "e1071", "caret" and "MultiscaleDTM" packages. This is the training command:

preds = list()
for(i in 1:nrow(train)){
train_data = train[-i, ]
test_data = train[i, ]
mod = svm(Rhodolith ~ APA170 + bathy + rug + SD, data = train_data, kernel="radial", type="C-classification",cost=3)
preds[[i]] = predict(object = mod, newdata = as.matrix(test_data[ ,c("APA170","bathy","rug","SD")]))
}

After I ran the functions, I received this message:

Error in model.frame.default(formula = Rhodolith ~ APA170, data = train_data, :
invalid type (S4) for variable 'APA170'

and

Error in model.frame.default(formula = Rhodolith ~ bathy, data = train_data, :
invalid type (S4) for variable 'bathy'

I thought it might be a class problem, but, no matter the command I use to find a difference between the datasets, I can't seem to find a reason why it shouldn't work.

Investigating "class", I get this:

class(APA170)
[1] "SpatRaster"
attr(,"package")
[1] "terra"
class(bathy)
[1] "SpatRaster"
attr(,"package")
[1] "terra"
class(rug)
[1] "SpatRaster"
attr(,"package")
[1] "terra"
class(SD)
[1] "SpatRaster"
attr(,"package")
[1] "terra"

And, "str", this:

str(APA170)
S4 class 'SpatRaster' [package "terra"]
str(bathy)
S4 class 'SpatRaster' [package "terra"]
str(rug)
S4 class 'SpatRaster' [package "terra"]
str(SD)
S4 class 'SpatRaster' [package "terra"]

Can someone please help me sort this out? Thanks in advance.