Why not Syz taoba liris iksa? I though iksa was "is".
The tense system in High Valyrian works differently than the English one. High Valyrian doesn't have any progressive forms, so "he is smiling" and "he smiles" are identical sentences, without a construction using a form of "to be".
I thought is was issa or not?
"Issa" is "he/she/it" is, yes. But in this case, "to be" is used as an auxiliary verb in English. "Sagon", the High Valyrian for "to be", is not used as an auxiliary verb. It's only used as a copula.