I find it very disheartening that you charge diamonds for required quest negotiations in the daily challenge. For my part I just do not do those and let it pass to the next day. Give us a break.
Diamonds are not required for quests
However if you don't have the resources for the quest they can be bought via diamonds. What you could do is look at your guild members ages. Figure out how far you have a continuous lineup of ages.
Now contact the highest age in that lineup and ask to buy some goods with FPs for trading down purposes. Trade down those goods through each age to your current age and some for the previous age as well. You'll now have enough goods for whenever a quest needs to negotiate
This is assuming it's a straight negotiation and not a map negotiation. If it's map negotiation you'll need goods for whichever sector age you're upto