If I fail an exam do I need to repurchase the proctoring service?

No. Unlike other providers, the proctoring service you purchase can be used on all your exam attempts in courses that are included in your package. As long as you have exam attempts available you can get the exams proctored without any additional charge. Other providers mostly charge a fixed fee for each proctored exam, and you need to pay again if you fail the exam and need to retake it.