Applications send a warning message if the received inputs from the user are invalid.
Is "are invalid" correct or should it be "were invalid"?
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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.