Testing coefficient difference in 2 probit models

[Dayuan Gu]

I would like to test the significance of difference between the coefficients in 2 probit models. I follow the code in Stata Manual:
. logit y1 x1
. estimates store M1
. logit y2 x2
. estimates store M2
. suest M1 M2
. test [M1]x1=[M2]x2

In my case, I re-phrased the above code:
. probit y1 x1 if group==0
. estimates store M1
. probit y1 x1 if group==1
. estimates store M2
. suest M1 M2
. test [M1]x1=[M2]x1

But I was only told by Stata that "equation M1 not found" so that I have to use "reg" model instead of "probit" to test the coefficient difference.
I am really thankful if anyone could kindly provide suggestions on the proper stata code. Thank you very much!