Learn Turkish: Bu platformda abonelik ücretini yılda bir mi ödüyorsun? - Do you pay the subscription fee once a year on this platform?

It follows the pattern taught in this lesson: a time period with the locative case suffix -da or -de, followed by bir (one). Literally meaning 'in a year, one', it is the standard way to express regular frequency. You can swap the time period to make phrases like haftada bir (once a week) or ayda bir (once a month).

Why is the question particle mi placed in the middle of the sentence instead of at the end?

The particle mi places the focus of the question on the word immediately before it. By putting it after yılda bir, the speaker is specifically asking about the frequency: 'Is it once a year that you pay?' If it were at the end (ödüyor musun), the question would just be whether you pay it or not.

Let's review ücretini. Why are there two -i suffixes at the end of this word?

The phrase abonelik ücreti (subscription fee) is a noun compound, so the first -i is the compound marker (a possessive suffix). Because this specific fee is the direct object of the verb ödüyorsun, we need to add the accusative case suffix. The -n- is a buffer letter separating the two vowels, and the final -i is the accusative marker.

Since this is about a regular, repeating action, why use the continuous tense ödüyorsun instead of the simple present (aorist) ödersin?