How to properly compare interacting levels

Interfaces brms
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Thanks so much for this! I am trying to make the model work, but I am getting an error message:

Error: Factors with more than two levels are not allowed as covariates.
So, following my example above, this is my actual model:

summary.brm.model_zero <- summary(brm.brm.model_zero <- brm(bf(DV ~
    0 + (T + L + S) * C +
    (1|Item) +
    (1|Participant),
        T ~ 0 + type,
        L ~ 0 + GroupsL,
        S ~ 0 + GroupsS,
        C ~ 0 + condition,
        nl=TRUE),
    prior=c(prior(normal(0, 0.5), nlpar=T),
            prior(normal(0, 0.5), nlpar=L),
            prior(normal(0, 0.5), nlpar=S),
            prior(normal(0, 0.5), nlpar=C),
            prior(exponential(1), class=sigma)),
    family=gaussian,
    data = dat,
    chains=4, iter=4000, cores=4,
    control=list(adapt_delta=.95)))

So, it interaction the problem here? Or?

Thanks!