Errata for "V. Blomer, G. Harcos, P. Maga, D. Milicevic, The sup-norm problem for GL(2) over number fields, J. Eur. Math. Soc. 22 (2020), 1-53." (9.16): In the expression for w_{l_1l_2}, the term x_{l_1}x_{l_2} should be multiplied by 1+\delta_{l_1\neq l_2}. In the expression for w_{l_1^2l_2^2}, the term x_{l_1^2}x_{l_2^2} should be multiplied by 1+\delta_{l_1\neq l_2}. Display before Lemma 14: "\cdot|\delta|_\mathbb{R}" should be "\cdot|\delta|_\mathbb{C}"