Learn Turkish: Makbuzu onaylanmayan misafirler kızgın görünüyor. - The guests whose receipts were not approved look angry.

This is a possessive relative clause. First, we have the possessed object with a possessive suffix: makbuzu (their receipt). Then we use the subject participle -(y)An on the verb: onaylanmayan (which is not approved). Finally, the noun being described: misafirler. Literally, the structure means the guests that their receipt is not approved.

Why is it makbuzu (singular receipt) and not makbuzları (plural receipts) since there are multiple guests?

In Turkish, when a group of people each has one of something (like one receipt per guest), it is very common to use the singular form for the possessed object. Saying makbuzları wouldn't be grammatically wrong, but makbuzu is much more natural here.

Can you break down the suffixes in the word onaylanmayan?

It starts with the noun root onay (approval). We add -la to make the verb onaylamak (to approve). Then -n makes it passive: onaylanmak (to be approved). The -ma is the negative marker. Finally, the buffer -y- and the relative clause suffix -an create the adjective form: onaylanmayan (which is not approved).

Why is görünüyor used here for look instead of bakıyor?