How can I run an IV model with fixed effect in a non-panel dataset? I know that in case of panel data, we would use -xtivreg2-.

I have a dataset where each row represents one childbirth delivery. I would like to estimate the effect of a municipality level policy which is believed to have affected a given variable X in different ways. Thus my key independent variable with be the interaction between X and a dummy for post-policy period. I would like to include municipality fixed effects as well as to cluster the standard errors at the municipality level.

If I would be to force a panel structure to my data, the panel variable would be each child born (which only shows up once in the dataset). Stata would not run the command:

Code:
. xtset id d_pos
       panel variable:  id (weakly balanced)
        time variable:  d_pos, 0 to 1
                delta:  1 unit

. 
. gen d_pos2 = d_pos

. 
. xtivreg2 peso d_pos2 (d_pc = trat), fe cluster(mun)
Warning - singleton groups detected.  6097656 observation(s) not used.
no observations
r(2000);

end of do-file

r(2000);

.