I have been studying [this preprinted paper][1] and the references therein. I believe that there are some typos; However, since I am not an expert yet, I would like to make sure I am correct.

I do not understand how the author made the restriction in the paragraph after equation (2.5)? in particular $ l \le 2j+2$. 


Thanks in Advance.

  [1]: https://arxiv.org/pdf/2107.01482.pdf