fix

transfer-tokens/src/processor.rs

@@ -25,7 +25,9 @@ pub fn process_instruction(
 ) -> ProgramResult {
     // Create an iterator to safely reference accounts in the slice
     let account_info_iter = &mut accounts.iter();
-    set_return_data(_instruction_data);
+    // Set return data to the integer value which increments for each transfer
+    let return_data = [0u8; 8];
+    set_return_data(&return_data);
     // As part of the program specification the instruction gives:
     let source_info = next_account_info(account_info_iter)?; // 1.
     let mint_info = next_account_info(account_info_iter)?; // 2.