Master password is rejected when deleting vault

Hi. I am having a problem deleting my Primary vault after transitioning from 1Password 6 to 1Password v7 (1P7). I upgraded my macOS app from 1P6 to 1P7 (I have both installed on macOS) and then followed the instructions on the following page in order to transfer my existing data to my 1Password account.

https://support.1password.com/migrate-1password-account/

I then tried to follow the instructions in the following step to set up my 1P app on iOS.

https://support.1password.com/migrate-1password-account/#set-up-your-other-devices

I migrated my account okay, but when I try to delete the Primary vault in the iOS app, I get a popup asking for my master password. I put in my master password for 1P7 (I changed it slightly when I upgraded), but it rejects my password. I tried putting in my old master password, the one I use for 1P6, and it also gets rejected. The master password I use for 1P7 on macOS works perfectly fine on the desktop app. I am not quite sure what I'm doing wrong. I'd like to transition over to use the 1Password subscription, but can't get past this step in the process.

On a slightly unrelated note, if I was using Dropbox to sync my passwords while using 1P6, and then transition to use 1Password's subscription service, do I need change any settings on the iOS app? Seems like my primary vault is still syncing w/my dropbox, but I suppose that will go away if I am able to delete the primary vault?

Thanks in advance to any help you can provide!

1Password Version: 7.0.6
Extension Version: Not Provided
OS Version: iOS 11.4
Sync Type: Not Provided