500 error after trying to inslal snapshot

ok Dimitris, I get this:
Server error status: Internal Server Error [500]

WE NEED YOUR HELP, BOSS!
×
Hang on a minute... It looks like your WordPress site isn't configured to allow one-click installations of plugins and themes. But don't worry! You can still install this plugin by entering your server's FTP credentials here:
FTP Username

soedevadm
FTP Password

•••••••••
FTP Host

srv1a.salesovereurope.com
CANCEL OKAY, CONTINUE!

We will remember these details for 15 minutes in case you want to install or, update something else.
Or you can enable one-click installations on this site by adding the following details to wp-config.php:
define( 'FTP_USER', 'your FTP username' );
define( 'FTP_PASS', 'your FTP password' );
define( 'FTP_HOST', 'soedev.com' );

It gives me the opportunity to fill in my password, but when I do it comes with the 500 error.
what to do? Piet.