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@alaser  the duplicate CP30 

(a) for joint filers each is sent a notice for the FULL amount.  ONLY the full amount  ( i.e. not the aggregate / double amount). 

(b) the CP30 should tell you where and how to pay -- the reason is the same as shown on CP30.

(c) you can always contact  IRS at the "contact number " shown on the front of the notice.  Whatever you do,    Do NOT IGNORE the timing  -- generally 30 days or whatever is shown on the notice.

Does this help ?  Is there more I can do for you ?