Q: Is there any fee concession policy for authors having no funding sources?
From what I understand, you wish to know if journals have any fee concession policy for researchers who do not have sufficient funds.
There are two different models of publishing: the subscription model and the open access model. Subscription journals do not require the author to pay anything, but the reader needs to pay to get access to the published article. The problem with this model is that your article will not get a wide outreach as journal subscription charges are quite high and generally only institutions can afford it.
The other model of publishing is open access in which the published article is freely accessible for readers, but the author generally has to pay a publication fee, also known as article processing charges. Article processing charges vary across journals and some journals have a very nominal fee. Additionally, not all open access journals charge APCs, and there are some not-for-profit journals that publish open access without charging the authors.
However, many open access journals have concession or fee waiver policies in place. Most of these journals offer concessions or fee waivers to researchers from low-income countries. Also, many open access journals consider fee waiver requests from authors who are under financial constraints. For example, many large publishing houses such as Nature Publishing Group, Elsevier, Springer, and BMJ have a fee waiver policy according to which fee waiver requests are considered on a case-by-case basis, and a total or partial waiver is granted at the journal's discretion.