how one is not accused of plagiarism when including an article in a MSc thesis?
Many journals have specific policies that allow the submission of material that has previously appeared in an MS or Ph.D. thesis.  This is an exception to the general rule that submitted manuscripts must consist of new, not previously published, research.
Similarly, many academic institutions have policies that allow for the inclusion of text from published papers in MS and Ph.D. theses if the journal publisher also allows this.
Assuming that both your institution and the journal that you're publishing in have such policies, then you can reuse a journal article in your thesis.  This is really quite common in many STEM fields. When you do submit your paper, you should make it clear that some or all of the paper has previously appeared in your thesis and refer to the publisher's guidelines on this.