I have a Bryant heater/air conditioner combo that the heater has stopped working. Here is what happens when I turn it on manually-

Smaller fan kicks on

I can hear the gas come on for a few short seconds

I can hear the igniter trying to ignite

It seems like it is not igniting and after a few cycles of this, I just shut it off. It has ignited a few times in between but it is not consistent.

Any idea on what it could be?

Inducer runs, and you hear gas delivery. Spark ignition, I assume? Check the electrode gap, spark lead, and ground integrity of the burner assembly and ignition module. Weak or inconsistent spark is likely the culprit.