I thought I would be able to add someone to the access list for my channel but I get "you cant perform that command" or something similar anyway? I am the channel owner @ #slack-stuff.

Make sure you're entering everything in the right order:
http://www.wyldryde.org/commands/chanserv.php#access

Yes, everything entered correctly. I have made sure to set myself as founder and sop. Still says "You can't use this command Use the AOP, SOP, HOP and VOP command instead. This is ok. I'll consider this solved. AOP and SOP is fine.

You can not add someone to the access list if 1. you are a half op 2. trying to add them to a level that is higher than what you are at, or lastly you have xop turned on or off. If XOP is off you have to use the access list /msg chanserv access #channel add nick level \\ levels: 3 = VOP, 4 = HOP, 5 = AOP, 10 = SOP, 10000 = q. On the other hand if the xop feature is on the command will be /msg chanserv {hop/aop/sop} #channel add nick. Also make sure that the nick you are trying to add to the access list has a registered nick.

Regards, David