Look at J. Bernstein, Erez Lapid - "On the meromorphic continuation of Eisenstein series", Journal of the American Mathematical Society (2023) Volume 37, Number 1, January 2024, Pages 187234.

(Also freely available as the preprint arXiv:1911.02342v3.)

Look at J. Bernstein, Erez Lapid - "On the meromorphic continuation of Eisenstein series", Journal of the American Mathematical Society (2023) Volume 37, Number 1, January 2024, Pages 187-234, MR4654611, Zbl 7752243.

(Also freely available as the preprint arXiv:1911.02342v3.)

Look at J. Bernstein, Erez Lapid On the meromorphic continuation of Eisenstein series Journal of the American Mathematical Society (2023) Volume 37, Number 1, January 2024, Pages 187234 https://doi.org/10.1090/jams/1020 arXiv:1911.02342v2 [math.RT] 27 Apr 2020

Look at J. Bernstein, Erez Lapid - "On the meromorphic continuation of Eisenstein series", Journal of the American Mathematical Society (2023) Volume 37, Number 1, January 2024, Pages 187234.

(Also freely available as the preprint arXiv:1911.02342v3.)