Regex_pars in brms

I am having troubles to extract all varying intercept-parameters for ID’s from a multivariate mvbind(variable1, variable2) brms fit object.
I am trying

matrixOfparameters ← as.matrix(brms_fit_object,

                  regex_pars = "r_id__variable1[\\,Intercept]")

but get ALL estimated parameters in my matrix. The same code works with univariate rstanarm fit-objects.

  • Operating System: Mac OS BigSur 11.6
  • brms Version: 2.16.1