Firstly, please read "How to not be a spammer" from Buddhism SE's Help center.
Any post (question or answer or comment) that exists solely to promote a site, product or service, and serves no other purpose, will be flagged as spam and deleted.
Also, this is a Q&A site, and not a discussion forum.
Genuine questions or answers that include third party links to support the post, may be acceptable, provided the author clearly discloses his or her affiliation. The reader should not have to click the link in order to understand the question or benefit from the answer. The question or answer should summarize the relevant contents from the link.
Buddhism-related non-profit sites, products and services may be promoted in the Buddhism SE chatroom, provided the author clearly discloses his or her affiliation. I have not seen any Stack Exchange rules prohibiting this so far.
As stated on this page, Stack Exchange also offers free community promotion ads for non-profit organizations.