Do you understand the reason a person must reject an antipope? A person must do this in order to remain in Catholic unity, since being subject to an antipope and recognizing their teachings as being Catholic and authoritative, while merely ignorant, and not invincibly ignorant
that the man is an antipope (as in the case of St. Vincent Ferrer, who is exonerated by common sense and the teachings of Pope Pius IX in Singulari Quadem, or Quadam as it's also been spelled) is a schismatic action.
Therefore if Pope Pius IX, for example, had been subject to an antipope, barring invincible ignorance, then he would have been a schismatic and an antipope himself. Trace that ripple effect all the way back to Boniface VIII and you would have nearly seven hundred and fifteen years of antipapacy, and you would have to reject the following six accepted Ecumenical Councils as non-Catholic robber Councils.
The Council of Vienne (1311-1312 A.D.)
The Council of Constance (1414-1418 A.D.)
The Council of Basel-Ferrara-Florence (1431-1445 A.D.)
The Lateran Council V (1512-1517 A.D.)
The Council of Trent (1545-1563 A.D.)
The Vatican Council (1869 A.D.)
Please answer this question:
If sixty four popes, from Blessed Benedict XI (1303-1304) to Pius X (1903-1914), accepted Boniface VIII as a valid Pontiff, how are you not schismatic for rejecting him, or how could you logically still accept these men as popes?
Hint: the only answer that is not schismatic is:
I was wrong