First of all, thank you to use one of my node-red nodes! I worked a lot on this node and i hope you'll enjoy my efforts in offering my work to all users.
If you're here, you may have some issues. I'm sorry about that.
Don't worry and relax, we'll find what your problem is, because the knx-ultimate node WORKS, it has about thousand installations around the world and i have it installed as well for my home. So please follow the FAQ and if you "i'm still having problem", contact me.

• Do you have created the Gateway configuration node with the IP and Port pointing to your KNX/IP Router/Interface?
• If you've a KNX/IP Router, you need to put in the Host field, the multicast KNX IP address 224.0.23.12 and port 3671
• If you've a KNX/IP Interface, you need to put in the Host field, the Interface's IP address, for example 192.168.1.22 and port 3671
• If you have two or more Ehternet interfaces (like Raspberry PI), either specify the Ethernet interface to use in the Gateway configuration node, or totally disable the WIFI interface. Remember to restart node-red!
• Use only certified pure KNX/IP Router (preferable) or pure KNX/IP Interfaces. Do not use "all in one" devices, or proxies, or devices that, besides other functions, do KNX/IP routing as well. A stable connection between LAN and KNX is the most important thing, and it need to work. Spend money on that and you'll setup and forget it.
• If you have an IP interface try to disable the ACK by selecting Suppress ACK request in the Gateway configuration node.
• Follow the I CAN ONLY RECEIVE TELEGRAMS, NOT SEND - OR VICE VERSA checklist
• If you're running Node-Red in a container, delay the start of node-red after the container boots up. Some users report that the Ethernet card is still DOWN when node-red starts. You can try it by manually stop node-red, disabling auto start of noder-red at boot, reboot the container, wait 2-3 minutes and manually start node-red. If KNX-Ultimate works, the issue is that.

• Read the THE NODE DOESN'T WORK faq.
• Check and eventually disable DDOS protection or UDP flood protection on your switches/routers. This as general rule. UDP KNX packets can be blocked otherwise.
• Try to directly connect your KNX/IP Router/Interface and your node-red PC.
• If you've a cheap KNX/IP Interface, specially if is an "all in onde" device, it can hangs. Go buy a real KNX/IP Router.
• If you use an KNX/IP Interface, be sure that you haven't reached the maximum connection limit (see your KNX/IP Interface's user manual). KNX/IP Routers are preferable instead, they doesn't have connection limits.

• If you're running knxd on the same machine of node-red, please use 127.0.0.1 as interface address, otherwise knxd will have problems.
• If you're using knxd, please check the filtering tables and change the KNX config-node's physycal address accordingly.
• Enable the Echo sent message to all node with same Group Address in the gateway config-node, under advanded options.

You may have other Node-Red KNX Plug-ins installed.

• Remove all KNX Plugin from node-red Palette. Leave only knx-ultimate. Remember to remove the config nodes as well, they are hidden.
• If you have an IP interface try to disable the ACK by selecting Suppress ACK request in the Gateway configuration node.

Your KNX/IP Router/Interface may have filtering active.

• Check in ETS if the router has filtering enabled. If yes, either allow forwarding in all configuration pages of your KNX Router, or change the physical address of the knx-ultimate config node according to your router's filter tables.
• If you're using knxd, please check the filtering tables and change the KNX config node physycal address accordingly.

• Make sure to use the right datapoint. For example, for temperature, use 9.001
• When possible, import the ETS csv file in the Gateway configuration node. You'lll have always the right Datapoints!
• Make sure not to have two or more knx-ultimate nodes, having same Group Address but different Datapoint.

• Enable the Echo sent message to all node with same Group Address in the gateway config-node, under advanded options.

Secure IP Router/Interfaces doesn't work if set to secure. It works, instead, if you allow unsecure connections to you router.

• Make sure to disable the secure routing or to allow unsecure connections.
• If you feel that you can be hacked, you can use a second ethernet card, straight connecting node-red machine to your KNX Router/Inteface with a dedicated LAN cable. In the knx-ultimate config node Bind to local interface option, you can then set this interface to be the default KNX/IP interface.
• Secure connection will be implemented one day.

Flood protection avoids your node-red UI to become unresponsive, due to a too high amount of messages sent to te input pin of the node in a specified time frame of 1 second.
The max number of msg you can send to a node is 120 each second. If you need to send a lot of msg to the node, please consider a "delay" node, to delay each message a bit.
See here

• Review your flow. Send less messages to the node or use a delay node.
• Use RBE filter, to discard messages having the payload equal to the current node's payload.

In a ETS installation, setting Datapoints is mandatory, at least for professional one.
With Datapoints, all youd visualization and control devices know how to handle the telegram and how to perform a right decondinf of values.
You'll see that ALL devices, control software, visualization systems and all the entire KNX world need Datapoints, so why not to thanks knx-ultimate, to force you to finally fix your ETS installation, that wait so long to be fixed? :-)

• Put an headphone on your head, with good music, open ETS and start adding datapoints.
• Or... import ETS file by selecting the option "if Group Address has no Datapoint", to "Import with a fake 1.001 datapoint (Not recommended)", or to skip affected datapoint.
• Remember to set the FULL datapoint (main type + subtype), otherwise the importer will set a default .001 subtype. Please see this image

Circular reference protection avoids your node-red UI to become unresponsive and your KNX installation to be flooded, by disabling two nodes with same Group Address link toghether.
For example, if you link the output pin of a node having Group Address 0/1/1, to the input ping of another node having the same Group Address 0/1/1, the protection will kicks in.
See here

• Review your flow. Detach the two identical nodes or out something inbetween, acting as "moderator".
• Use RBE filter, to discard messages having the payload equal to the current node's payload.

• Open an issue on Github. Whenever you open an issue, i receive an email and i can sort it out immediately.
• Send me a PM on Knx-User-Forum. I'm here as TheMax74. Mein Deutsch ist nicht so gut, daher bitte auf Englisch schreiben!