Applications send a warning message if the received inputs from the user are invalid.
Is "are invalid" correct or should it be "were invalid"?
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.
It could depend on the rest of the sentence; you need to be careful about matching the tenses between the different clauses. However, in most cases, either "were invalid" or "are invalid" would be OK.
If I were programming this,
I hope this is helpful. This is one of those cases where different people would handle it in different ways, and there's really no "wrong" answer.