It is recommended to sacrifice the camel when it is standing and tied

Ziyad b. Jubair reported that Ibn 'Umar came upon a person who was slaughtering (sacrificing) his camel and had made him kneel down. So he told him to make it stand up festered (and then sacrifice it) according to the Sunnah of Prophet ﷺ.

حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، أَخْبَرَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، عَنْ يُونُسَ، عَنْ زِيَادِ بْنِ جُبَيْرٍ، أَنَّ ابْنَ عُمَرَ، أَتَى عَلَى رَجُلٍ وَهُوَ يَنْحَرُ بَدَنَتَهُ بَارِكَةً فَقَالَ ابْعَثْهَا قِيَامًا مُقَيَّدَةً سُنَّةَ نَبِيِّكُمْ ﷺ .