Moving wordpress from one server to another

I am trying to move a WordPress website from my dev server e.g. https://www.devserver.com.au/site to production server https://www.productionsite.com

I have gone through this linkl https://codex.www.ads-software.com/Moving_WordPress but nothing is workign for me.

Please advise me, I have been doing below so far

1. Download your existing site files i.e https://www.devserver.com.au/site
2. Export your database – go in to MySQL and export the database.
3. Move the backed up files and database into a new folder – somewhere safe – this is your site backup.
4. Log in to the site you want to move and go to Settings > General, then change the URLs., I have changed it to https://www.productionsite.com
5. Download your site files again.
6. Export the database again.
7. Edit wp-config.php with the new server’s MySQL database name, user and password.
8. Upload the files.
9. Import the database on the new server

I am getting below error

website page isn’t working
website is currently unable to handle this request.

I know the link says When your domain name or URLs change there are additional concerns.
So how can I fix it , I don’t have access to dashboard now.
If I have to make changes in the database then HOW?