Error: mis-match in nbr endpoints in model & in data

[pascalschulthess]

I'm getting the following error where I don't quite know why it is happening:

Error in .configsaem(model = .model, data = data, inits = .inits, mcmc = rxode2::rxGetControl(ui,  : 
  mis-match in nbr endpoints in model & in data

I have a dataset with IV and SC dosing where I set CMT=Ad for all SC entries and CMT=Ap for all IV entries. The model does have multiple states:

States ($state or $stateDf): 
  Compartment Number Compartment Name
1                  1               Ad
2                  2               Ap
3                  3              Avs
4                  4              Ais
5                  5              Aln

And I just have

# Concentration
        Cp <- Ap/Vp + BL

        # With error
        Cp ~ add(a) + prop(b)

at the end. So there's just one output. Why does the method think that there are more outputs in the dataset? Or how does the dataset need to look like to clear this error?
Thanks!

[pascalschulthess]

I already found the solution :)
In the dataset only the dosing rows need to match the compartment names while the observation rows need to be set to model output. More specifically:

   EVID CMT  
  <dbl> <chr>
1     1 Ap   
2     0 Cp   
3     1 Ad