you tried ads and that should work, see regex101
The pihole documentation contains very usefull info for creating regexes, your specific question explained here (example domain).
A common mistake, when entering a new regex is NOT to select the regex tab, before entering your regex. What you enter on the domain tab will be converted, what you enter on the regex tab will remain unchanged.
Finally, your regex should be assigned to a group (default = Default // see groupmanagement / domains), that contains the client you want to be affected.
The debug log (available local at /var/log/pihole_debug.log) contains all the information to determine what makes things work / fail, which is why jfb asked you to upload it.