> m2 <- clm(categorical_FOD_FODs ~ 0 + Condition_FODs:Gender_FODs - 1, + random = ~1|subject, data = indvar_FODs) > summary(m2) formula: categorical_FOD_FODs ~ 0 + Condition_FODs:Gender_FODs - 1 data: indvar_FODs link threshold nobs logLik AIC niter max.grad cond.H logit flexible 3321 -2910.89 5847.79 6(0) 1.75e-12 1.4e+03 Coefficients: (1 not defined because of singularities) Estimate Std. Error z value Pr(>|z|) Condition_FODsA:Gender_FODsFemale 0.32677 0.33910 0.964 0.335 Condition_FODsB:Gender_FODsFemale 0.03530 0.33820 0.104 0.917 Condition_FODsC:Gender_FODsFemale 0.08655 0.33833 0.256 0.798 Condition_FODsD:Gender_FODsFemale 0.11344 0.33915 0.334 0.738 Condition_FODsA:Gender_FODsMale 0.30283 0.33753 0.897 0.370 Condition_FODsB:Gender_FODsMale -0.06136 0.33716 -0.182 0.856 Condition_FODsC:Gender_FODsMale -0.02626 0.33692 -0.078 0.938 Condition_FODsD:Gender_FODsMale 0.29300 0.33773 0.868 0.386 Condition_FODsA:Gender_FODsNon-Binary / Genderqueer 0.65051 0.45817 1.420 0.156 Condition_FODsB:Gender_FODsNon-Binary / Genderqueer 0.27418 0.44615 0.615 0.539 Condition_FODsC:Gender_FODsNon-Binary / Genderqueer 0.22538 0.44405 0.508 0.612 Condition_FODsD:Gender_FODsNon-Binary / Genderqueer NA NA NA NA Threshold coefficients: Estimate Std. Error z value ascending|descending 0.1625 0.3235 0.502 descending|identity 2.8620 0.3299 8.677 (199 observations deleted due to missingness) Output indicates that one coefficient could not be estimated due to singularities. The log-likelihood, AIC value, and some convergence diagnostics are also displayed. How should I edit the the code to overcome this issue?

library(ordinal)
m2 <- clm(categorical_FOD_FODs ~ 0 + Condition_FODs:Gender_FODs - 1, 
          random = ~1|subject, data = indvar_FODs)
> summary(m2)
formula: categorical_FOD_FODs ~ 0 + Condition_FODs:Gender_FODs - 1
data:    indvar_FODs

 link  threshold nobs logLik   AIC     niter max.grad cond.H 
 logit flexible  3321 -2910.89 5847.79 6(0)  1.75e-12 1.4e+03

Coefficients: (1 not defined because of singularities)
                                                    Estimate Std. Error z value Pr(>|z|)
Condition_FODsA:Gender_FODsFemale                    0.32677    0.33910   0.964    0.335
Condition_FODsB:Gender_FODsFemale                    0.03530    0