If you are unable to pay interest on your mortgage, it is important to speak with your lender as soon as possible. Depending on the specific terms of your loan and the specifics of your financial situation, they may be able to provide you with some leeway or a payment plan that works for both parties. However, if you are unable to make payments due to long-term financial difficulties, it is advisable to seek professional advice from an independent financial advisor in order to gain more insight into potential solutions.