Non-linear specification (variable is not a valid distributional or non-linear parameter)

Interfaces brms
3

Thank you very much!

Here’s is an (unprincipled) reprex:

# load packaged
library(dplyr)
library(brms)

# Some fake data
Data <- expand.grid(r = factor(c(1:5)),
                   t = factor(c(1:8))
                   ) %>%
        mutate(C = round(rnorm(nrow(.),500, 150)),
               D = round(rnorm(nrow(.),10000, 1000)),
               R = C/D,
               Srt = rnorm(nrow(.),0.5, 0.15))

# Non-linear formula
bform <- bf(
        Srt ~ I,
        I ~ 1 + (C * B) + (1|r) + (1|t),
        B ~ 1 + (a * R(...^b) + c),
        a ~ 1,
        b ~ 1,
        c ~ 1,
        nl = TRUE
)

# Get available priors
get_prior(bform,
          data = Data,
          family = Beta())

This gives the following error:
Error: The parameter 'B' is not a valid distributional or non-linear parameter. Did you forget to set 'nl = TRUE'?