PHP/LAMP on Server A, MySQL on Server B - Database connection always tries to connect to Server A

Hi,
I am trying to setup a project on a server:
in ProjectSettings/Targets, I set up Webserver / PHP via SFTP to Server A.
Thats working so far.
I chose this as target.
When I try to set up a Database Connection in Server Actions/Connection Options,
I set MySQL and the Server Adress to the host name of “ServerB” (my MySQL hosted on a different system= Server B).
Used the specific db name and db username correctly.
When I say “Test connection” it always says falsely throw an erro:
“Error using this Database Connection”, Server response Acces denied for user ‘dbuser’@‘serverA’ - instead of @‘serverB’.
Why is that?