
This is what actually should work I must be declaring my variables incorrectly. The issue I'm having is that what you refer to as lin , I tried calling a few things, from b to LinPred (which worked in the link here: brms issue 47). When I've tried doing this, I receive errors that say "The following variables are missing from the dataset....[insert variable used to symbolize linear part of the model)". But I believe you're code is on the right path for what needs to be done I'll try altering my syntax to be sure it resembles yours let you know if it works.

SaaSHub
SaaSHub  Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives
NOTE:
The number of mentions on this list indicates mentions on common posts plus user suggested alternatives.
Hence, a higher number means a more popular project.
Related posts

[Q] Correlated multivariate Beta model

[R] Are there methods for ridge and lasso regression that allow the introduction of weights to give more importance to some observations?

Package for :Generalized Mixed Effects Models for ZeroInflated Negative Binomial distributions ?

Multiple observers

Bayesian Structural Equation Modeling using blavaan