What do they mean for setting up amazom jailbroken fire stick Enter the charatets asthey are given in the challenge

logically that would mean capitals when capitals and small letters when small letters
this information is case sensitive so if you use lower case letter ( small ) when the character is a upper case ( capital) then it will not accept what you enter

Down near bottom.
Should be a capita box with random numbers /letters.
Enter them in blank box, hit ENTER.Z

Its asking for the password challenge to make sure its YOU who is trying to access your account...

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Please contact Amazon customer service for this problem.

What the heck is a enter the characters as they are given in the challenge???

you have to enter it exactly as is on the card