Netweaver ABAP: SSL Server - self-signed certificate

I recently tried to create a self-signed certificate by my own CA. In short: It failed.

I wonder if anyone has done such a setup before? It is only for test purposes, I planned to import the CA into my mobile so that I can connect to the S/4HANA through browser (e.g. Fiori Launchpad) in a way that the browser wouldn't complain about the certificate of S/4HANA being insecure/ not trusted (I know I can override this). Also, Android/iOS wouldn't allow to connect to un-trusted HTTPS in the background (which is what I do through an app).

My intended steps:

1. Create a CA through openssl - that worked
2. Import the CA into Netweaver - not sure if this is done through STRUST? I could import it but which part of the STRUST tree is correct?
3. Create a certificate signing request (CSR) from the SSL server tree in STRUST. - worked.
4. Sign the CSR by my CA with openssl - worked.
5. Import the signed .crt into STRUST - error: "Chain of certificates is incomplete"

Any idea how to achieve it? Obviously I'm missing a link.