Fallback to single entry with minfee if no estimates

src/server.tsx

@@ -424,6 +424,11 @@ function calculateFees(mempoolFeeEstimates: MempoolFeeEstimates, esploraFeeEstim
   const minFee = (mempoolFeeEstimates?.minimumFee ?? FEE_MINIMUM) * 1000;
   logger.debug({ message: 'Using minimum fee: {minFee}', minFee });
 
+  // If we didn't manage to get any fee estimates, return a single estimate with the minimum fee.
+  if (Object.keys(feeByBlockTarget).length === 0) {
+    return { 1: minFee }
+  }
+
   // Return fees filterd to remove any that are lower than the determined minimum fee.
   if (minFee) {
     return filterEstimates(feeByBlockTarget, minFee);