وَأَوْفُوا۟ بِعَهْدِ ٱللَّهِ إِذَا عَٰهَدتُّمْ وَلَا تَنقُضُوا۟ ٱلْأَيْمَٰنَ بَعْدَ تَوْكِيدِهَا وَقَدْ جَعَلْتُمُ ٱللَّهَ عَلَيْكُمْ كَفِيلًا ۚ إِنَّ ٱللَّهَ يَعْلَمُ مَا تَفْعَلُونَ ﴿٩١﴾
当你们缔结盟约的时候，你们应当履行。你们既以真主为你们的保证者，则缔结盟约之后就不要违背誓言。真主的确知道你们的行为。
Haram Speech & character
Is swearing a false oath haram?
Short answer
Yes. The Quran warns against breaking oaths after making them firm (16:91), and warns those who sell Allah's covenant and their oaths for a small price (3:77). Swearing by Allah on a lie, in order to take money or a right, is a major sin.
Evidence
Quran
إِنَّ ٱلَّذِينَ يَشْتَرُونَ بِعَهْدِ ٱللَّهِ وَأَيْمَٰنِهِمْ ثَمَنًۭا قَلِيلًا أُو۟لَٰٓئِكَ لَا خَلَٰقَ لَهُمْ فِى ٱلْءَاخِرَةِ وَلَا يُكَلِّمُهُمُ ٱللَّهُ وَلَا يَنظُرُ إِلَيْهِمْ يَوْمَ ٱلْقِيَٰمَةِ وَلَا يُزَكِّيهِمْ وَلَهُمْ عَذَابٌ أَلِيمٌۭ ﴿٧٧﴾
以真主的盟约和自已的盟誓换取些微代价的人，在后世不获恩典，复活日，真主不和他们说话，不睬他们，不涤清他们的罪恶，他们将受痛苦的刑罚。
This is general information, not a fatwa. For your own situation, ask a qualified scholar.
Questions about halal and haram
Is swearing a false oath haram?
Yes. The Quran warns against breaking oaths after making them firm (16:91), and warns those who sell Allah's covenant and their oaths for a small price (3:77). Swearing by Allah on a lie, in order to take money or a right, is a major sin.