Hi, and welcome.

Could you post a reproducible example, called a reprex, please?

Also, there's a there's a community guideline concerning homework, FAQ: Homework Policy, that you should be aware of for reference.

How does your case differ from the example in the documentation?

```
library(plm)
data(Wages)
ht <- plm(lwage ~ wks + south + smsa + married + exp + I(exp ^ 2) +
bluecol + ind + union + sex + black + ed |
bluecol + south + smsa + ind + sex + black |
wks + married + union + exp + I(exp ^ 2),
data = Wages, index = 595,
random.method = "ht", model = "random", inst.method = "baltagi")
summary(ht)
#> Oneway (individual) effect Random Effect Model
#> (Hausman-Taylor's transformation)
#> Instrumental variable estimation
#> (Baltagi's transformation)
#>
#> Call:
#> plm(formula = lwage ~ wks + south + smsa + married + exp + I(exp^2) +
#> bluecol + ind + union + sex + black + ed | bluecol + south +
#> smsa + ind + sex + black | wks + married + union + exp +
#> I(exp^2), data = Wages, model = "random", random.method = "ht",
#> inst.method = "baltagi", index = 595)
#>
#> Balanced Panel: n = 595, T = 7, N = 4165
#>
#> Effects:
#> var std.dev share
#> idiosyncratic 0.02304 0.15180 0.025
#> individual 0.88699 0.94180 0.975
#> theta: 0.9392
#>
#> Residuals:
#> Min. 1st Qu. Median 3rd Qu. Max.
#> -12.643736 -0.466002 0.043285 0.524739 13.340263
#>
#> Coefficients:
#> Estimate Std. Error z-value Pr(>|z|)
#> (Intercept) 2.9127e+00 2.8365e-01 10.2687 < 2.2e-16 ***
#> wks 8.3740e-04 5.9973e-04 1.3963 0.16263
#> southyes 7.4398e-03 3.1955e-02 0.2328 0.81590
#> smsayes -4.1833e-02 1.8958e-02 -2.2066 0.02734 *
#> marriedyes -2.9851e-02 1.8980e-02 -1.5728 0.11578
#> exp 1.1313e-01 2.4710e-03 45.7851 < 2.2e-16 ***
#> I(exp^2) -4.1886e-04 5.4598e-05 -7.6718 1.696e-14 ***
#> bluecolyes -2.0705e-02 1.3781e-02 -1.5024 0.13299
#> ind 1.3604e-02 1.5237e-02 0.8928 0.37196
#> unionyes 3.2771e-02 1.4908e-02 2.1982 0.02794 *
#> sexfemale -1.3092e-01 1.2666e-01 -1.0337 0.30129
#> blackyes -2.8575e-01 1.5570e-01 -1.8352 0.06647 .
#> ed 1.3794e-01 2.1248e-02 6.4919 8.474e-11 ***
#> ---
#> Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
#>
#> Total Sum of Squares: 243.04
#> Residual Sum of Squares: 4163.6
#> R-Squared: 0.60945
#> Adj. R-Squared: 0.60833
#> Chisq: 6891.87 on 12 DF, p-value: < 2.22e-16
```

^{Created on 2019-11-24 by the reprex package (v0.3.0)}