Shevuos 4:7

If a person calls upon witnesses to testify for him that he is a kohein, a Levi, not the son of a divorcee or not the son of a woman who performed chalitzah, or that another person is a kohein, a Levi, not the son of a divorcee or not the son of a woman who performed chalitzah, or that another person raped or seduced someone (possibly referring to the accused’s own daughter), or that his own son wounded him, or that another person wounded him or set fire to his haystack on Shabbos – in all of these cases, witnesses who falsely deny having information are exempt (because these are capital cases).

Shevuos 4:8

If he calls them to testify for him that the other party said he would give him 200 zuz but he reneged, they are exempt. This is because witnesses are only liable for denying knowledge in a case where the claim resembles a deposit.