פירוש על שבועות 4:2

וחייבין – a sliding-scale offering (this offering is made when there are one of three transgressions where the financial situation of the sinner is taken into account in determining the nature of the sin-offering that he brings: violating an oath, taking a false oath to avoid giving testimony and entering the Temple or partaking of sacrifices while ritually impure. The sinner generally brings a sin-offering of a female lamb or goat, but if he cannot afford it, he may instead bring a pair of doves, one as burnt offering and the other as a sin-offering or a if he cannot afford even that, he may instead bring a meal-offering).

And they are liable for intentional transgression of the oath, and for its unintentional transgression coupled with intentional [denial of knowledge of] testimony, but they are not liable for unintentional transgression.
And what are they liable for the intentional transgression of the oath? A sliding scale sacrifice.
This mishnah continues the lists we have seen in the previous three mishnayoth.
There are two elements to the false oath of testimony: 1) knowing information and intentionally withholding it; 2) intentionally swearing falsely that one does not know the information. The mishnah teaches that if the witnesses intentionally deny knowledge of the testimony, even if they don’t realize that swearing falsely is forbidden, they are liable for intentionally swearing falsely. However, if they don’t realize that they know information then they are not liable, since this was a totally unintentional transgression. In other words, there punishment hinges upon their intentional denial of knowledge of information. If they intentionally withheld information and swore to it, then they are liable to bring a sliding scale sacrifice, as described in Leviticus 5:5-13.

על זדון השבועה – for it did not state concerning it "ונעלם" /that he concealed or hid one’s self.

ועל שגגתה עם זדון העדות – that they known that the this oath was forbidden but they did not know that they are liable for a sacrifice for it.

ואין חייבים על שגגתה – if they are completely in error inadvertently, for they were forced, we don’t call them "ונשבע על השקר"/that they swore falsely.