Green’s Dictionary of Slang

(US) to confuse, to bewilder, to confound, to botch.

1867		G.W. Harris Sut Lovingood’s Yarns 206: I’ll bet yu my shut agin that ar momoxed up roas’in har, that hits chawed into dish rags.
1909		L.W. Payne Jr ‘Word-List From East Alabama’ in DN III:v 350: mommux (up), v. To botch, spoil in the making. ‘He mommuxed up that house’ [...] To mix badly, confuse utterly. ‘He got all mommuxed up on that job.’.
1953		Randolph & Wilson Down in the Holler 266: The fellow momoxed the job.