Do the adhkar become void if a Muslim inadvertently makes a mistake in them, and will he be rewarded for them?

If the heart is heedless while reciting the prescribed remembrances (adhkar) and the remembrance is confined to the tongue, then the one who performs it is hoped to receive reward, but not like the reward of one who remembers with both their heart and tongue. If a mistake occurs by changing the wording of the remembrance, it should be repeated, because the wording of the prescribed remembrances is divinely ordained and fixed.