Reçete üzerindeki yazım hatası düzeltilmeden ilaç verilemez.

The suffix -ki turns a locative phrase into an adjective or relative clause.
• üzerinde = “on it” (locative of üzer)
• üzerindeki = “that which is on (something).”
You then use it before a noun (here yazım hatası) to specify “the mistake that is on [the prescription].”

Because the sentence refers to the mistake being corrected (passive), not someone correcting.
• düzelt = “to correct”
• -il = passive marker → düzeltil- (“to be corrected”)
• -me = negative → düzeltilme- (“not to be corrected”)
• -den = ablative/adverbial “from/without” in the converb form → düzeltilmeden = “without being corrected.”

-meden is the negative adverbial (converb) suffix meaning “without doing X.”
In düzeltilmeden, it expresses “without (the mistake) having been corrected.”

verilemez is the negative passive form of vermek (“to give”):
• ver- = root “give”
• -il- = passive → veril- (“to be given”)
• -me- = negative → verilme- (“not to be given”)
• -z = 3rd person singular aorist ending → verilmez = “(it) cannot be given” or “(it) is not given.”

-sı is the 3rd person singular possessive suffix.
• yazım hatası literally = “its writing mistake,” i.e. “the writing/spelling mistake.”
Possessive suffixes also signal definiteness, so no separate article (“the”) is needed.

Turkish has no separate indefinite article, but you can use bir (“a”).
• bir yazım hatası = “a writing mistake.”
Adding bir makes it clearly indefinite instead of the definite sense in the original sentence.