Is a sale deed valid without specified payment and money transfer?

The buyer has registered a plot based on a 20-year agreement with the seller, without any payment made by the buyer to the seller. However, the sale deed states that the seller has agreed to receive the full payment, yet no mode of payment is specified. The seller transferred the property in good faith based on the prior written agreement but has requested that the buyer pay any applicable income tax. The buyer asserts that there will be no income tax liability as no money transaction has occurred. However, the transaction amount is recorded as paid to the seller in income tax documents. Is this sale deed valid given the absence of a specified payment method and the lack of any money transferred from the buyer to the seller? What options does the seller have to recover the tax amount that is due?