Related Clues:

• Run up a bill, say
• Be obligated to pay
• Word that's a homophone of its first letter
• 'I ___ you an apology'
• Middle of IOU
• The 'O' in IOU
• Use credit
• What the middle of 58-Across stands for
• Be in a red state, perhaps
• 'I ___ you a call'
• "What do I ___ you?" ("How much is this?")
• Have to settle later
• Have charge card balances
• Still need to pay back
• Be a little shy?