Most of you who have been using iPhone for a long time may not know that you can use 2 or multiple Apple IDs on your account. Though it is always convenient to use a single Apple ID but then some users prefer to use multiple IDs for some truly valid reasons, for example if you want to keep a different apple ID associated with your credit card so that any one pretty younger in your house should not buy anything on your iPhone without telling you (believe me kids often do that, but then while doing lots of users face issues while updating some applications or reinstalling an already bought application.
When you use multiple Apple IDs to buy applications from App Store then you must know that an ID which was used at the time of buying this application will be used again at the time of updating it. Let us say that you have an ID ‘xxxx’ which you is your primary ID used on your iPhone to use the services like FindMyiPhone or iCloud or to install any application which is free and not there is another ID ‘yyyy’ which is used by you only when you need to buy a paid application.
Every time your iPhone will be logged in with ‘xxxx’ ID, i.e. if you will go to settings then Store and then Apple (the iPhone screen has been mentioned below) you will find that you have been logged in with that ID but if you will try to update a paid application (which has been bought using ‘yyyy’) then a popup windows will appear asking the password of ‘yyyy’ account (though you were logged in with ‘xxxx’ ID). You can update that application you that ID only, other alternative can be deleting that application from your iPhone and then buying that again using your present ID ‘xxxx’.
As mentioned above in the screenshot, if you want to change the account then you can tap the sign-out option and then sign with the other ID for paying paid stuff. Now if you are using iTunes then you will have to tap the apple ID as mentioned below in the screenshot and then you can change the ID to use it.
Please note that if you have already bought an application using ‘xxxx’ ID and then deleted it after using it, then the status of that application for that ID in App Store will be ‘INSTALL’, if you have not downloaded or bought that application ever then the status will be ‘FREE APP’ or ‘x.xx$ BUY APP’ and if the app is already installed on your iPhone then its status will be ‘DOWNLOADED’. If you download any already bought application (which has been deleted) then you will not have pay again. But if you download an application (which was bought by ‘xxxx’) with ID ‘yyyy’ then you will have to pay for that application.
So, be very cautious while using multiple IDs on your iPhone, as they may confuse you. Please let us know if you face any other issue related to password handling in multiple IDs.