When you don’t know your spouse’s income and can’t find out through reasonable means, the CRA recommends that you enter your best estimate. You can then come back to it before Netfiling to correct the amount from each other's return.  

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This is incorrect. Any number put into the box does not let me move to the next page. It makes me try again and never works regardless of what amount I put in.

Same here, anyone has a solution? Thanks

@Weilanweilan 

Line 23400 less Line 23500 equals Line 23600. So, if your spouse didn't have any social benefit repayments, then Line 23400 is the same as Line 23600. Line 23400 is not on the detailed summary; you will see it on your T1.