I've been struggling to perform placebo test and finding p-values after running a synthetic control method. The results i got are:
Loss: Root Mean Squared Prediction Error


---------------------
RMSPE | 1.404323
---------------------
------------------------------------------------------------------------------------------------------------------------
Unit Weights:

-----------------------
Co_No | Unit_Weight
----------+------------
1 | 0
2 | .133
3 | .491
4 | .271
5 | .105
6 | 0
7 | 0
8 | 0
9 | 0
10 | 0
11 | 0
12 | 0
-----------------------
------------------------------------------------------------------------------------------------------------------------
Predictor Balance:

------------------------------------------------------
| Treated Synthetic
-------------------------------+----------------------
domtaxtogdp | 7.438928 5.893027
Agricultureforestryandfishi | 33.42571 14.0593
Debtserviceonexternaldebtt | 3.14e+08 3.72e+08
BroadmoneyofGDP | 29.42877 45.3518
Debtserviceonexternaldebtt | 3.14e+08 3.72e+08
Exportsofgoodsandservices | 35.71216 35.86212
Foreigndirectinvestmentneti | 3.793209 5.617001
Importsofgoodsandservices | 53.39756 52.23179
Inflationconsumerpricesannu | 18.47533 13.05279
TradeofGDP | 89.10973 88.09391
GDPpercapitacurrentUS | 639.9211 1818.518



When i try to run a placebo test with the following command:

tempname resmat

forvalues i = 1/12 {

synth taxtogdp domtaxtogdp Agricultureforestryandfishi BroadmoneyofGDP Debtserviceonexternaldebtt Exportsofgoodsandservices Foreigndirectinvestmentneti GDPpercapitacurrentUS Importsofgoodsandservices Inflationconsumerpricesannu taxtogdp(2000) taxtogdp(2018) taxtogdp(2005) , trunit(`13') trperiod(2010) xperiod(2010(1)2018) keep(test`i')

matrix `resmat' = nullmat(`resmat') \ e(RMSPE)

local names `"`names' `"`i'"'"'

}

mat colnames `resmat' = "RMSPE"

mat rownames `resmat' = "names"

matlist `resmat' , row("Treated Unit")

I get
invalid syntax
r(198);

.
. mat colnames `resmat' = 13 "RMSPE"
matrix __000009 not found
r(111);

.
. mat rownames `resmat' = 13 "names"
matrix __000009 not found
r(111);

.
. matlist `resmat' , row("Treated Unit")
__000009 not found
r(111);

Any help with what I might be doing inaccurately?