Do I need to pay my employer after I resign?

I started a healthcare job in January of 2025. The pay was terrible and not able to cover my bills and gas. I was driving over 10 hours a week with no gas or mileage compensation so with that I decided to go work at a higher paying job with benefits. Here is where my question lays. I signed a contract stating “If employee does not maintain employment for the minimum of six months after becoming certified, employee will be responsible for repayment of course cost and registration fees(est. $650.00+ & registration fee) to —— insert employer here” Now I haven’t gotten my certification or had the agency pay my registration fee yet. So do I have to pay them as I just put in my two weeks and received an email with an invoice of $650.00. I don’t think I do as I never got the certification but I am unsure