The sandal of the Prophet ﷺ had two straps.  

أَنَّ نَعْلَ النَّبِيِّ ﷺ كَانَ لَهَا قِبَالاَنِ  

Anas bin Malik brought out for us, two sandals having two straps. Thabit Al-Banani said, "These were the sandals of the Prophet ﷺ ."  

ثَابِتٌ الْبُنَانِيُّ هَذِهِ نَعْلُ النَّبِيِّ ﷺ