get_df with the the betwithin method

[YibiaoLiang]

Hi, I have a glmer model and try to get the degree of freedom with the betwithin method. The model looks like this
model1 <- glmer(R1 ~P1 + (1|ID)+(1|trial),data = ABD, family = poisson)
But when I tried to use get_df(mixConTime,type="betwithin"), it shows the error

Error in out[which("(Intercept)" != parameters)] <- ddf[term_assignment] :
replacement has length zero

I want to know how to use this method, but I can't find the example on the Internet. Thank you!