Responsa for Yevamot 209:15

Q. A levir performed the rite of halitzah with a shoe sewed with flaxen thread, but which did not belong to him. The levir refuses to repeat the rite with another shoe. The law provides that halitzah performed with a shoe not belonging to the levir is valid bediabad (after the act has been performed). What does bediabad mean in this case; does it mean after the rite was performed, or only after the woman remarried?
A. Bediabad, in this case, means after the rite was performed. Nevertheless, the aforementioned performance of the rite is invalid, for a different reason: the shoe used was sewed with flaxen thread and, therefore, was never fit for this purpose. Since, however, the levir performed an invalid rite of halitzah, neither he nor his brothers are now permitted to marry the widow. Halitzah by the same levir being the only manner of releasing her, he may be forced, by persuasion or by flagellation, to repeat the rite with the proper shoe. For now the Mitzvah revolved on him alone, and we are permitted to scourge a Jew until he perform the required Mitzvot.
This Responsum is addressed to Rabbi Menahem of Würzburg.
SOURCES: Am I, 93, 94.