You are lying to me.
Okłamać / Okłamywać calls for the accusative case, as opposed to Kłamać / Skłamać that calls for the dative case, correct? Why is it? Unfortunately asking ChatGPT such questions about why the nature of case usages is completely futile 
In simple terms, the o- prefix acts like the english “to”, or maybe “at”, so it takes a direct object which is then in the accusative case.
If you translate “okłamać” as “to deceive” it maybe makes it easier to see why it takes a direct object.
“kłamać” without prefix is actually intransitive and just means “to lie”. I don’t know enough polish to judge whether “kłamać” takes a dative object, as you say, despite being intransitive?
English has the archaic verb “to belie” which inherits the “be-” prefix with a similar function from its germanic roots. See (belie - Wiktionary, the free dictionary), etymology 2, meaning #5.
German still also has both “lügen” (to lie, intransitive) and “belügen” (to lie to someone, transitive).
See also (o- - Wiktionary, the free dictionary) #3 where the english “be-” prefix is mentioned.
Thanks for such an insightful response! Your doubts about kłamać/skłamać taking an object in the dative are well founded, as I couldn’t find anything on wiktionary to back my previous comment, that was one of the alternatives that are selectable on DeepL, so it’s better we take it with a grain of salt.