That is not how the Value-for-Value (V4V) model of Nostr works:
"Value for Value (V4V) is an economic model on Nostr where information is provided free of charge directly to users without paywalls or middlemen, allowing recipients to voluntarily give value back if they find the content useful."
Instead of asking for a specific amount, you let the audience voluntarily decide what your work is worth to them after they consume it. The value is what you provide, not what you receive.