Can't Add, Delete, Update Plugins after migration

I’ve tried to search for this and have not felt comfortable with the results cause of the age of the post(s) or not seeing exactly the same problem.

These problems come after a migration from one server to another and use of a new URL.

Updates seems to be happening in the same way as usual but take a long time with the browser busy effecting the change. Then the dashboard says it is done “successfully” only to show in the plugins it still needs to be done.

On WordPress plugin Adds or installs, I’m getting confirmation that it has been installed.
Then I get this message when I try to activate it.
“The plugin does not have a valid header.”

Delete of a plugin gets one of two things. First the message that the plugin is removed but it is not when I inspect the list of plugins.

OR I get this message . . . .
“Plugin could not be deleted due to an error: Could not fully remove the plugin(s) event-espresso.3.1.15.P/espresso.php.”
(This message came with Event Espresso plugin attempting to delete older version. This happens with all plugins. Removal can be done through ftp.)

I’ve had to input FTP username and password before being allowed to attempt to install, update, or delete a plugin.

The Webhost said it has a “secure (or “hardened”) php, by default”.

I hard coded this into the wp-config.php to bypass that.

[ Moderator Note: Please post code or markup snippets between backticks or use the code button. ]

//*added ftp login credentials to avoid WordPress asking for FTP details every time I wanted to upgrade a plugin*
define('FTP_HOST', 'ftp.thewebsite.com');
define('FTP_USER', 'ftp_user_name');
define('FTP_PASS', 'ftp_user_password');
//*If you can use a SSL connection set this to true*
define('FTP_SSL', true);

Thanks in advance for the help.