I just found out that in order for the following method to work correctly,
a client that supports omemo protocol, its advertised entityCapabilities must include the PEP_NODE_DEVICE_LIST_NOTIFY
public static final String PEP_NODE_DEVICE_LIST_NOTIFY = PEP_NODE_DEVICE_LIST + "+notify";
Are the two features below also need to be included in the buddy advertised entityCapabilities,
or they belong to the xmpp server supporting features to be advertised.
public static final String PEP_NODE_DEVICE_LIST = OMEMO_NAMESPACE_V_AXOLOTL + ".devicelist";
public static final String PEP_NODE_BUNDLES = OMEMO_NAMESPACE_V_AXOLOTL + ".bundles";