Field 5508 is HBP repayment income. It is a supporting field for field 12900 of T1. It is used when you need to contribute RRSP to repay HBP, but you didn't contribute enough RRSP in tax year to repay it. So this part of HBP repayment shortage will be regarded as RRSP income.
Try to enter an amount into field 12900 of T1, it will pop up a supporting window. Field 5508 is the one for HBP repayment.
Tags: F5508, HBP