Difficulty Computing Simple Slopes with Reference Level "B" in Linear Regression Model

Question

I need to check whether the interactions i have found are significant. When I follow this line of codes, I do not have any issues. The simple_slopes(model) command is working. I ahve three conditions, 1 dependent variable, and a moderator.

m3  <- lm(dv ~ cond+ indiC+ cond*indiC + genderc, data=re);   
summary(m3);  
standardCoefs(m3);   
simple_slopes(m3)

However, when I switch to this model for the same variables

mm3  <- lm(dv ~ relevel(cond, ref ="B")+ indiC+ relevel(cond, ref ="B")*indiC + genderc, data=re);   
summary(mm3);  
standardCoefs(mm3)

the simple_slopes() command wont work. I have a significant interaction in the third condition compared to the B. So, how do i check it?

ı receive this message from R:

Error in `[.data.frame`(new_grid, , var) : undefined columns selected after trying simple_slopes() using the second regression.