Why would I go from getting money back to owing money after my returns were accepted?

the most common taxpayer errors are not indicating they received EIP3 (stimulus) and/or the advance child tax credit. you should get a letter of explanation from the IRS but this can take 2 to 4 weeks, you could try calling the iRS but its phone lines are swamped so you'll likely have difficulty getting through

"Accepted" doesn't mean that your tax return is correct or that your refund is approved. It just means that your tax return is ready for the IRS to start processing it. If, in the course of processing, the IRS finds an error, they may correct the error. The correction could result in reducing your refund or even changing it to a payment due.