How to Get Into Professional iOS development?

I’m trying to break into the iOS developer industry but I’ve been having some difficulty. I have 4 apps published to the iOS store (1 in Objective-C, the rest in Swift), I’ve applied to a few companies so far (I would estimate that I’ve applied to about 30). I’ve gotten callbacks from 2 remote positions, and 1 position based in New York. The initial phone screening interviews go well but for one of the remote jobs, they said they would like to see more apps on my portfolio, which drove me to create 2 more apps. The other remote company had a devskiller coding challenge which didn’t go well. The technical interview for the New York company was just questions related to iOS development and design patterns. After the interview, the New York company said they wanted someone with more professional iOS developer experience so I’m wondering:

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What should I be learning about to have a better chance of passing iOS developer interviews?

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what can I do to improve my chances of getting an iOS developer position?

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If you’re an iOS developer, how did you get a position as an iOS developer?

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is it just a case of I need to apply to more positions?

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Thanks in advance for the help and support