XMPP: Start issue "Unexpected server repsonse"

[Huppi]

When I start the Bifrost with my configuration to the XMPP server, it fails to connect to the XMPP server with the Error "Unexpected server response".
On the XMPP Server Side I see the following flow:

Received from Bifrost:
<stream:stream xmlns:stream="http://etherx.jabber.org/streams" to="[xmpp-domain]" version="1.0">

XMPP Responding:
<error xmlns="urn:ietf:params:xml:ns:xmpp-streams"><invalid-namespace></invalid-namespace><text xml:lang="en_US">one of the two namespaces must be present: jabber:client or jabber:server</text>

Received from Bifrost:
<?xml version="1.0" encoding="UTF-8"?><handshake xmlns="jabber:component:accept">5436b3c30ec9db5dc2b2a0e0d7393032f4a77853</handshake>

XMPP Responding:
<?xml version="1.0" encoding="UTF-8"?><error xmlns="urn:ietf:params:xml:ns:xmpp-streams"> <unsupported-stanza-type/> <text xml:lang="en_US">could not process incoming stanza</text> <handshake xmlns="jabber:component:accept">5436b3c30ec9db5dc2b2a0e0d7393032f4a77853</handshake> </error>

---

The Bifrost start.sh output is this:
> [email protected] build
> tsc

ERROR: ld.so: object './node_modules/node-purple/deps/libpurple/libpurple.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
ERROR: ld.so: object './node_modules/node-purple/deps/libpurple/libpurple.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.

> [email protected] start
> node --enable-source-maps lib/Program.js -c config.yaml --port 3642

ERROR: ld.so: object './node_modules/node-purple/deps/libpurple/libpurple.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
ERROR: ld.so: object './node_modules/node-purple/deps/libpurple/libpurple.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
DEBUG 07:34:52:779 [LogWrapper] Reconfigured logging
INFO 07:34:52:783 [cli] Loading config file /etc/matrix-bifrost/config.yaml
WARN 07:34:52:973 [NeDBStore] Starting integrity check
WARN 07:34:52:974 [NeDBStore] Check WILL modify database
INFO 07:34:52:976 [NeDBStore] Found 1 room entries, 0 of which are invalid
INFO 07:34:52:981 [NeDBStore] Found 0 user entries, 0 of which have no type
INFO 07:34:52:985 [NeDBStore] Also found 0 invalid ghosts
INFO 07:34:52:985 [Program] Selecting xmpp-js as a backend
INFO 07:34:52:988 [RoomAliasSet] Loaded 1 regexes
INFO 07:34:53:000 [Program] Enabling metrics
INFO 07:34:53:006 [Program] Checking if homeserver is up
INFO 07:34:53:079 [Program] Started appservice listener on port 9555
INFO 07:34:53:263 [Program] Successfully pinged the bridge. Round trip took 173ms
INFO 07:34:53:267 [Program] Ensuring bot is registered
INFO 07:34:53:293 [Program] Bridge has started.
INFO 07:34:53:298 [XmppJsInstance] Starting new XMPP component instance to xmpp://[xmpp-server]:5222 using domain [xmpp-domain]
INFO 07:34:53:303 [XMPP-conn] status: connecting
INFO 07:34:53:307 [XMPP-conn] status: connect
INFO 07:34:53:308 [XMPP-conn] status: opening
INFO 07:34:53:441 [XMPP-conn] status: open
ERROR 07:34:53:448 [XMPP-conn] Error: Unexpected server response
at Component.authenticate (/etc/matrix-bifrost/node_modules/@xmpp/component-core/lib/Component.js:38:13)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at Component.<anonymous> (/etc/matrix-bifrost/src/xmppjs/XJSConnection.ts:21:17)
ERROR 07:34:53:451 [Program] Encountered an error starting the backend: Error: Unexpected server response
at Component.authenticate (/etc/matrix-bifrost/node_modules/@xmpp/component-core/lib/Component.js:38:13)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at Component.<anonymous> (/etc/matrix-bifrost/src/xmppjs/XJSConnection.ts:21:17)

What's wrong here?