Host 'XXXXXX-xxx' is not allowed to connect to this MySQL server (no replies)

Hello,
Writing C# I always get the error "Host 'STATION1-W10' is not allowed to connect to this MySQL server".
I use QNAP NAS MySql->myphpadmin.

When establishing the connection and testing it, it is successful.
But when running the code I get this error message when trying to open the DATABASE (e.g. connString open(); ).

Checked privileges in myphpadmin and all is good

Need HLP.
THANK YOU.