quantum field theory - Is there a mistake in a QFT textbook

I tried to calculate one of the problems in the textbook Gauge Theory of Elementary Particle Physics by Ta-Pei Cheng and Ling-Fong Li. On page 248 you can find the following calculation of a loop

Quantum Field Theory by Franz Mandl

Quantum Field Theory Demystified - Paperback By McMahon, David - VERY GOOD 9780071543828

Peeter Joot's Blog » Quantum Field Theory

What Is a Quantum Field Theory? | Mathematical physics

Quantum Fluctuations and Their Energy – Of Particular Significance

David Tong: Quantum Field Theory

Quantum Field Theory: A Tourist Guide for Mathematicians

Providing a comprehensive introduction to quantum field theory, this textbook covers the development of particle physics from its foundations to the

Quantum Field Theory and the Standard Model

What is the most difficult book to learn quantum field theory? - Quora

Sabine Hossenfelder: Backreaction: Quantum Mechanics is wrong. There, I've said it.

Quantum Field Theory: 9780471496847: Mandl, Franz, Shaw, Graham: Books

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Quantum Field Theory ✓ Applications and Implications

Which courses before GR and QFT?