The spell you are trying to augment must be in the domain in question.
Since all your domains share the same domain slots, it would be more proper to say "the spell you're trying to extend must be on your domain list". If only he mentioned in the OP that he had travel domain. Oh, wait, he does. If only he - oh, look, longstrider, travel 1.
You have to have the metamagic feat in question.
He was asking if he could use his metamagic feat. Of course he has it.
You have to use up a level appropriate available domain spell slot.
You mean, like, a second level slot for a first level spell? As stated in the OP?