I solved this one. Instead of filtering for the URL-parameters as they appear in the browser (e.g. groups%5B0%5D), which does not work, I now filter for the “translated” parameters (e.g. groups[0]). And it works as advertised. No regular expressions needed.
Re: Capture multiple parameters in Custom Dimensions
We are evaluating several avenues. If and when we find a suitable solution, I will post it here.
Thank you @heurteph-ei for your help. Very helpful and much appreciated!
For multiple values in a custom dimension, we are discussing several avenues. Right now, collecting the data externally and then importing them to Matomo seems most promising. But it will take some programming effort and hence, time …
Matomo does not seem to offer a solution for capturing multiple values from one URL. By design you can only capture one per custom dimension and URL.
So, we are considering using something else than Matomo for the capture and then importing the data to Matomo to have it all in one place for a more convenient analysis.