These are the options I can think of:
Discuss uses a link to a donate page. You can set up an Open Collective, PayPal or other landing page somewhere and add the link on your forum using FoF Links.
Some communities, for instance https://hockeybulletin.se, use subscriptions as a way for users to support the community. In return they receive access to a badge and possibly private tags. These run on https://extiverse.com/extension/blomstra/payments
