Exactly... Don't close an app to move to another, leave it open and open an additional app and switch back and forth between the two. if you don't close the one with the code, a new code will not be generated and you can switch back and forth between the two to achieve the results desired.
I spent about 3 hours this last week trying to figure out why my Uncle couldn't make phone calls using his Echo dots, with voice command. Turned out he had already done all of the setup properly, but the way he was issuing commands to Alexa were sketchy and sometimes a bit hard to understand, and his phone contacts were all named oddly in his contact list on his iPhone. when he asked to call someone by name, he didn't;t include all of the words on their listing.
Example: Calling his youngest son (contact list showed as Son Barrett [LASTNAME], to help with emergency identification of his relatives he named all of his contacts similarly). When he was trying to call, He would ask Alexa to Call Barrett, where Alexa immediately knows no one with that name, due to his listing. He had to go in and change all of his contacts with similar listings to simple listings for Alexa to understand who to call.
There are some really cool easy ways to use iPhone to set up proper contacts with the relationships as well. I did mine using "Hey Siri" to tell which of my contacts were my Wife, My Daughter, My Mother-in-law, My Uncle, etc... This is the easiest way I found at least. I don't know how it works with Android devices but I would think it wouldn't be much different... May have to go inland manually add relationships...
Setting up all these things can be a mess. What I find odd is I don't remember having to set up communications at all on my echo devices... I probably instinctively did something that made it possible during a set up of a device or skill or something, without even knowing what all I had enabled.
I keep telling myself how cool this stuff is... and just looking back to the 1970's for reference of how crazy fast our technologies have grown in both private and commercial ways.
To close out this whole rambling post, I will go back to the original post and say : The problems most encounter doing any of this set-up and usage, is easily looked up buy typing the problem or concept or question into the address bar at the top of all of the browsers... and hit the enter/return button on your keyboard. (this applies even to browsers on your phone)