How to deal with the factor variable?

[XUEbaogai0101]

dca(Surv(ttcancer, cancer) ~ risk_group, 
    data = df_surv, 
    time = 1,
    thresholds = seq(0, 0.50, by = 0.01),
    label = list(risk_group = "Prediction Model")) %>%
  plot(smooth = TRUE)

Error in `dplyr::between()`:
! Can't combine `x` <character> and `left` <integer>.
Run `rlang::last_trace()` to see where the error occurred.