Cargo planes arrival

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Ok, got it explained here

Got BRI going, but no cargo

Hi, I started Bari some days ago, have some S, M and the two L stands working. With the income I bought a M cargo stand but I never get a plane. I also unlocked the second arrival slot but I never get two planes in holding, not even a pax plane, so it seems kind of useless. Then I thought I had to buy the second terminal for cargo to be handled but no. So what am l doing wrong?