Hey, jodie.
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First of all these 5 characters are now jointly connected to the same login & password; and should I remove one of these characters, I've completely lost it forever as it cannot be put back & I no longer have a way of getting it into game. Correct?
It isn't possible to remove a character off of a Jagex account once it has been added. The process is currently irreversible. There has been rumours that, maybe, just maybe, they will add a feature in the future that may or may not allow you to "archive" characters that you no longer wish to utilize.
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Original message details are unavailable.
After the 6-digit code is entered you get a popup screen on computer that has ten 8-digit codes on it. Right this down or copy it somewhere.
\tThe next time you login to either the game or RS site you will need one of those codes. At such time you get the message you have used one of the codes. After using all 10 codes you will need to return to your account settings on RS and request 10 more codes. (This means using the phone again to scan the QR code..big white box..getting the 6-digit code that you type into computer screen to get 10 more authenticator codes.)
No, that is not correct. Those are backup codes -- See:
https://help.jagex.com/hc/en-gb/articles/5410794084497-Backup-codes
-- that Jagex provides you with when setting up two-step authentication via an authenticator app on your Jagex account. These are to be used when and if you lose access to the authenticator app that you just added to your Jagex account. Once you set up two-step authentication via an authenticator app, you ought to use the 6-digit code that is generated on that specific authenticator app to log in to your account whenever prompted.
This Support page is very useful too:
https://help.jagex.com/hc/en-gb/categories/4403516390801-Jagex-Accounts