Non WWW to WWW

I edited my ‘home url’ to ‘https://www.myfirstsite.com’

Those boxes at Settings > General tell WordPress what to expect coming and what to use for finding things, but they do not control what actually comes in to be recognized. So, you need to deal with that beforehand:
https://forum.ait-pro.com/forums/topic/htaccess-redirect-www-to-non-www-htaccess-redirect-non-www-to-www/

same problem with me, thanks for the solutions, i will try

Hello,

if it’s generally working fine, there might be a problem with links which are hard-coded (specified manually) and not controlled by site_url or home (url). In that case, try using Velvet Blues Update URLs plugin. It goes through your database and replaces all occurrences of the old url with the new one.

@rastislav Lamos,

Thanks for this.

It is generally working fine if I set it to this:
wordpress url: https://myfirstsite.com/site1
home url: https://www.myfirstsite.com

However, is it possible to set it to this instead?:

wordpress url: https://www.myfirstsite.com
home url: https://www.myfirstsite.com

Or is it impossible because Site1 is installed in a subdirectory instead of root?