Thanks to this comment I found out there was indeed this configuration:

            <plugin>
                <groupId>org.sonatype.plugins</groupId>
                <artifactId>nexus-staging-maven-plugin</artifactId>
                <version>1.6.13</version>
                <configuration>
                    <serverId>ossrh</serverId>
                    <nexusUrl>https://oss.sonatype.org/</nexusUrl>
                </configuration>
            </plugin>

but it was located in the parent pom.xml.
Everything works as intended now.