No constraint works in tobit

[Henry Strawforrd]

I am trying to impose a constraint in a tobit regression and since it did not work I tried to impose a simpler one but whatever constraint I impose it does not work. Why might that be?

Here is an MWE

set seed 12553
clear
set obs 1000
gen y = runiformint(0,10)
gen x = runiformint(0,1)
gen z = abs(rnormal() * 50)
gen inter = x*z

constraint define 1 (x=0)
constraint dir

tobit y x z inter, ul(10) ll(0) constraint(1)

[Henry Strawforrd]

It was the brackets around the constraint!