Dear Stata users,

I'm using STATA 16.0 to develop recreational demand function via using NBSTRAT model. I have several factor and continuous variables that force me to use "xi:" prefix in the model syntax because "nbstrat" is user-written command which is not allowed to use factor variables without this prefix.
Here is the code that I use:

Code:
  xi: nbstrat S8_y i.Ad S6_RC_En S13_dogal S13_engelli S13_profil S15_RC_Tek i.S31_RCTip S33_RC_Yesil i.S38_Arac S7_yil S14_Ortak S14_Alis S14_Engel S14_Guvenlik S16_Mal S23_puan S34_uzak S36_Gelir, vce(robust)
I obtain acceptable beta coefficients as output, however, I also want to compute marginal effects of each predictor that's why I use the code below:

Code:
margins, dydx(*) vce(unconditional)
But unfortunately, I have an error as:

Code:
   . margins, dydx(*) vce(unconditional)
    cannot compute vce(unconditional);
    predict after ml could not compute scores
    r(322);
Why does the model give this error? and How can I fix it? or what can be the alternative ways to get marginal effects without changing the model syntax?

I will appreciate it if anyone helps me with that issue.

Kind regards