I have 2 years of experience in manual testing, and I am currently learning automation testing in my spare time.
Great, try and implement some of the techniques you are using in your spare time at your work too. This will lead to a great deal of success at learning and speed up your manual testing process drastically. My primary cause for Automation at most of my positions was more to set up data how I needed it than to actually test anything with the automation. This WILL lead to pay raises, more job security and will look a lot better on a resume/interview than I learned it in my spare time.
I was thinking that will getting a foundation/entry testing certification really help me in promotions and increase my salary or just increase my knowledge and nothing more?
Gaining knowledge is always a positive. I will never recommend to someone to not gain knowledge in their field. Is the certificate itself worth it? Probably not honestly, but if it teaches you something and helps to validate that you are experienced in the field, it can be useful. The only way I see it being beneficial as a certificate would be if you and another candidate are viewed as equals it might be the boost you need for the position.
Even if I wish to try to get certified and pass the exams, is it too late or can I try after a few more years?
I would recommend doing this as soon as possible if you are going to. A lot of the courses cover the basics that if you wait a few years for it will essentially just either reinforce what you already know or tell you that your habits that have already been well formed are incorrect.
Overall, SQA is a very skilled position and most managers and recruiters respect that it requires a mentality that is difficult to find. A lot of the instincts that are required can not be taught or transferred. The pieces that transforms someone from being decent to great in this field is that inquisitive nature. Because of this, I see a lot of the certificates as purely self validation and the knowledge gained being the beneficial part.