503 errors while creating a new python web application

I am new to this cpanel. When I am creating a new python web application. There are only 3 options of python version for me which are 2.7.18, 3.7.12 and 3.8.6, If I am choosing the 3.7.12 and 3.8.6, the 503 error will be displayed but it works fine with 2.7.18 version. I cannot figure out this problem. Does anyone able to help me or give any documentation for me? I haven't put my source package inside this application but it already have this 503 bug. If anyone met this problem before please guide me to solve this. Thank you!