That’s an odd use of SNMP but if it works I bet a full writeup with the hardware and software config would be appreciated by the community. Most people use MQTT to publish or use REST API calls or the like. If the board supports SNMP it probably supports something like this.
OK, so that error means what it says. You have a syntax error on line 9 column 5 of test.rules so OH is rejecting the whole file. The error goes on to say that “DoorButtons” is not a valid symbol to exist at that position on that line of code.
Your best bet to find and solve syntax errors that are not immediately apparent is to use VSCode with the openHAB extension. https://docs.openhab.org/configuration/editors.html#openhab-vscode
You didn’t give the Group an aggregation function. What is it supposed to do with all of the members to generate the Number that DoorButtons gets set to? https://docs.openhab.org/configuration/items.html#group-type
Where did you get this syntax? https://docs.openhab.org/configuration/rules-dsl.html#event-based-triggers
There is no such thing as an Item group trigger. It is just:
Item DoorButtons received update
This is the root source of your syntax error. But the lack of an aggregation function will be a problem as well. By default OH will use EQUAL as the aggregation function which I’m pretty sure will result in an error because true/false are not valid states for a Number Item.
That is because a Group is an Item. There is nothing special you need to do to use it as an Item. It just has some extra stuff it can do.