Upgrade from 7.15.7 to 8.18.3 with 503 on AuthorizeUpgrade

Questions
1

I upgraded from umbraco 7.15.7 to 8.18.3. The application installed 8.18.3 through nuget and the database was 7.15.7. Then I started the application and the login page appeared, as shown below,

enter image description here
enter image description here1752×572 79.6 KB

Note that the browser address is:

http://localhost:59491/umbraco/AuthorizeUpgrade?redir=%2Finstall%2F%3Fredir%3Dtrue%26url%3Dhttp%253a%252f%252flocalhost%253a59491%252f#/login/false?returnPath=%252Fcontent

Meanwhile, a 503 error appears in the console, as follows:
enter image description here

If continue to enter the user name and password, will have the following request, but will still get a 503 error
enter image description here

I saw a similar problem. According to the operation, I didn’t solve the problem. What should I do to complete the upgrade? Many Thanks.

Regards,

Ray

This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/109125-upgrade-from-7157-to-8183-with-503-on-authorizeupgrade