Estimates fees for a sponsored (gasless) transaction.

This endpoint provides fee estimation for transactions where the relayer will pay the network fees on behalf of the user. The user pays fees in a token of their choice (e.g., USDC) instead of the native network currency (e.g., XLM for Stellar).

The endpoint accepts either a pre-built transaction XDR or a set of operations to build a transaction from. It returns the estimated fee amount in the specified fee token and the conversion rate from the native currency.