Possibly, quick acceptance for publication Two days ago, a physics journal received my manuscript and today they informed me that the editor and reviewer accepted my manuscript for publication. this is the first time for me publishing a manuscript, but two days, isn't that quick?
and they told me that I will pay around 700 Euros for the first installment.
I really need your advice here, I am afraid of getting screwed.
It is very unusual for a paper to be reviewed and get accepted in two days. Of course, there are some exceptions such as:


Solution to a very well known and long studied problem (even in this case, it is highly unlikely for the review process to be completed in 2 days).
Dramatically improving the conditions of a current crisis (e.g. a vaccine for COVID-19 outbreak)
Very short 


Other than these extreme cases, I, personally would not choose to publish in that journal, let alone pay for the publication.

Also, you can check this famous list for future considerations.