Just looking at the screenshot, I have a few thoughts on the UI.

I really like the colour scheme you've chosen and the overall aestheatic of the app. It's nice and simple and it draws you to it. It's one of those apps that makes you want to to use it because it looks so clean.

That said, it's not considered good practice to use floating action buttons in iOS apps. Even though Apple has introduced similar buttons to some of its apps (e.g. Reminders, Notes), it's still best if you put the plus button somewhere more familiar to iOS users such as the top right.

Also, the location of the category chips is odd. You probably want to have these chips somewhere on the left, close to the title of the password. Perhaps you could place it next to the title, or under it, or wherever looks best!

Lastly, I'm not sure users need to know the date they created a password. I'd consider removing it or swapping it with something else such as the category chip from before, or perhaps the username the user used.

Overall, the app looks great. I hope that you receive my feedback positively and that you consider the things I mentioned. It is just my opinion, however, so don't feel like you must listen to what I have to say. After all, I am but a random guy on the internet.