Combine the min/max of inputNumeric with Shinyvalidate rules

Question

I would like to disable the button if any field is out of range or contains non-numeric characters or is empty. If a field is in this condition I would like the red "!" within a circle to appear in the field.

The code below has the red circle appearing but the button is enabled.

If I change max = 1000 for inputId = a then the invalidation of the button occurs but no red ! for a value of say 350.

How do I get the red ! and the disabled button at the same time? Another issue with the code below is that if you enter 500 in Field A and then 500 in Field B the red ! in Field A disappears. This doesn't occur if shinyvalidate is not used.

library("shiny")
library("bslib")
library("shinyjs")
library("shinyvalidate")

per_month <- "/mth"
num_min <- 0
num_max <- 300

ui <- bootstrapPage(
  useShinyjs(),
  

  theme = bs_theme(version = 5, "font_scale" = 1.0), 
  div(class = "container-fluid",
      
      div(class = "row",
          div(class="col-4", 
              numericInputIcon(
                inputId = "a",
                label = "A",
                value = 100,
                min = num_min,
                max = num_max,
                width = "160px",
                icon = list(NULL, per_month)
              ),
          ),
          div(class="col-4", 
              numericInputIcon(
                inputId = "b",
                label = "B",
                value = 200,
                min = num_min,
                max = num_max,
                width = "160px",
                icon = list(NULL, per_month)
              ),
          ),
      ), 
      div(class = "row",
          div(class = "col-12",
              actionButton("cc_calculate", "—— Submit ——")
          ), align = "center"
      )
  )
)

server <- function(input, output, session) {

  iv <- InputValidator$new()

  iv$add_rule("a", sv_required(message = ""))
  iv$add_rule("a", sv_between(num_min, num_max, message_fmt = ""))
  
  iv$add_rule("b", sv_required(message = ""))
  iv$add_rule("b", sv_between(num_min, num_max, message_fmt = ""))
  
  iv$enable()
 
  observe(
    if (iv$is_valid()) {
      enable("cc_calculate")
    } else {
      disable("cc_calculate")
    }
  )

}

shinyApp(ui = ui, server = server)