Hello Jocelyn Houin, welcome to Microsoft Q&A forum.
First, please make sure you are trying to submit the repair request through the correct channel, which is the Microsoft Devices page.
Regarding the error you are seeing, the message “HTTP Error 500.30 – ASP.NET Core app failed to start” indicates a server‑side problem, and there would be no fix on your side.
If the correct page is truly down, you should either contact Microsoft Support directly at https://support.microsoft.com/home/contact, or, if possible, visit a Microsoft‑authorized service center for in‑person assistance. You can check the locations here: https://support.microsoft.com/en-us/surface/service-centers-for-in-person-support-fa81797b-44e0-47e5-b2f9-c490f9d330b4