what could be the problem when one of the coefficients from the linear regression model is not displayed in a coefficient plot? i would appreciate your kind help, as i have been wrecking my head and could not come up with a solution. so let us say that

reg dv iv1 iv2 iv1#iv2,ro

so when i plot it in a coefficient plot using coefplot, all the coefficients are displayed with an exception of the interaction term.

thank you