A typical FX forward trade would settle the foreign currency 2 days after the fixing of the FX rate. The forward leg of this trade would be priced by discounting in the domestic currency the value of the FX forward rate obtained through non-arbitrage.
In case the payment delay is much greater than 2 days, we may expect a convexity adjustment in the pricing formula. I struggle to find in the literature a formula for this convexity adjustment. I'd appreciate your input into this, for instance with a toy model or approximated formula.