could not find function "konfound_lmer"

[leRequinRomain]

1. When attempting to use konfound_lmer(), the following error is generated: "could not find function "konfound_lmer".
2. Also, when using konfound(lme4::lmer(), categorical_variable) with categorical variables I get the following error: "Error in if (!(std_err > 0)) { : argument is of length zero"

Any ideas how to resolve?
Can the functions be used with categorical variables in lmer() models?