Subject Firebird 3.0 client does not work with remote Firebird 2.5 database

On Debian Jessie with Firebird 2.5 I’m able to connect to a third party remote Firebird database. However on Debian Stretch with Firebird 3.0 installed I’m unable to connect to the same server with the same credentials. If I try to connect I get:

"Statement failed, SQLSTATE = 08004
connection rejected by remote interface”

Any help appreciated!