Pay your premium from your own bank account or credit card, then request the money back:
• Go to the Reimbursements tab in your dashboard
• Select Request reimbursement
• Choose Insurance premium, and attach documentation of the payment (this can be your SSA letter)
This is also how to handle a Part B premium that comes out of your Social Security check.
Reimbursements aren't automatic. Submit one each month so you're using that month's health budget.