I am co-authoring a physics manuscript with some students and colleagues. The results in this has been obtained by means of a grant to which multiple people have participated.Because the main research project reported in the grant proved to be too hard, we switched to a backup project, which is the subject of the paper.
One of the authors just asked me to include as an author one of the persons who contributed to the grant writing, even though this person made no scientific contribution to the paper, because of the subject switch above.
Is it fair and honest to include this person?
I am asking because if I feel like this is not fair, but if I refuse, this would put me in a difficult situation with the colleague who asked, potentially ruining our future collaborations with him. What should I do?