Android Question Avoid Unknown Sources Message during App Installation?

Hello All,
I am very new to the great B4A and I finished an App and I would like to publish it so, I tried to sign it through B4A <Tools-Private Sign Key> but I got a message as per following:

Signing package file (private key). Error

jarsigner: Certificate chain not found for: Zakarias. Zakarias must reference a valid KeyStore key entry containing a private key and corresponding public key certificate chain.


so, I went to have a self sign key through following command line:
E:\jdk-14.0.1\bin>jarsigner -verbose -sigalg SHA256withDSA -digestalg SHA1 -keystore keyNMEG.keystore myapp.apk b4a
after that I got the following message
>>> Signer

[trusted certificate]

jar signed.

Warning:
The signer's certificate is self-signed.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

but when I tried to install the app on Samsung S6 it is also still not trusted and give unknown sources message
so, what I should do more to let my app be accepted by any device?

Thank you very much