1. Check your old keystore file by going to TOOLS->PRIVATE SIGN KEYS.
If it is using DSA like below then NOT ACCEPTED FOR NEW APPS.
Signature algorithm name: SHA1withDSA
Subject Public Key Algorithm: 1024-bit DSA key
2. New apps must use 2048 bit RSA key and algorithm like below. Create a new keystore with the B4A IDE.
Signature algorithm name: SHA256withRSA
Subject Public Key Algorithm: 2048-bit RSA key
Therefore, all your new apps will use this keystore going forward