The term "declaring invalid" implies that something has been deemed ineffective or nullified. Some antonyms that could be used in place of this phrase may include "validating," "affirming," "ratifying," or "sanctioning." These terms suggest that the subject in question has been confirmed as valid or legitimate. Other options might include "upholding," "acknowledging," or "endorsing," which also communicate a sense of support or approval. Conversely, antonyms for "declaring invalid" might include terms like "valid," "effective," or "authorized," which suggest that the subject in question has been deemed acceptable or legally binding.