If you are unable to pay an article processing charge, you are likely to retain the right to make your 'accepted manuscript' open in your institutional repository: 'green' open access.
The SHERPA partnership of UKHEIs, funded by Jisc, maintains a number of online services to support open access publishing, including:
A key part of publishing open access material is ensuring that readers understand what permissions they have for re-use of the material. The Open Access Scholarly Publishers Association offers best practice guidelines on licensing and attribution in open access:
Beware of predatory publishers who "lie about their business practices for the purpose of attracting paying authors" (Rick Anderson, 2019). If you receive an unsolicited invitation to submit a paper to a journal you don't recognise, treat it with suspicion.
Think. Check. Submit. is a tool developed by scholarly publishers and societies, to offer researchers a checklist that will help them decide if a publisher is trustworthy: