What it is
The legacy Montgomery GI Bill buy-in: $100 per month for your first 12 months of service if you enrolled. Most members now use the Post-9/11 GI Bill, which has no buy-in, so this line mostly appears on older accounts or specific elections.
2026 rate
$100 per month for 12 months, $1,200 total, only if enrolled.
What goes wrong
It should stop at exactly 12 payments. A thirteenth month of MGIB deduction is a straightforward error worth a finance office visit.