鉄板 てっぱんネタではありませんでした
teppannetadewārimasendeshita

Noun
Desu Copula

The polite, past negative form of 鉄板ネタ

1. It wasn't a sure thing.; It wasn't a guaranteed success.; It wasn't a reliable topic.

Past/Perfective
Negative
Polite
Formal Register