Inclusion Bayes Factors when the factor is included in random slope

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I am trying to calculate inclusion bayes factor using ‘bayesfactor_inclusion’ function in R.
But when I include the random slope of a fixed factor, like in ‘brm(DV ~ A+B+(1+A|C))’, where DV stands for dependent variable, A and B are two fixed factors, and C is a random factors, the inclusion bayes factor can only be calculated for B but not A.
I wonder if I am doing wrong and if there is any solution!