While entering a Stock symbol, an error 13 Type mismatch occurs if the entered data is not read by Excel as a valid Stock data. This can be easily resolved easily by following the below steps:

1. Select the cell that contains data that is not identified as a stock data as shown below

2. Now go to Data ribbon and select "Stocks" under Data Types as shown below: 

3. And if a Question mark (?) mark is shown before the symbol, then Right-Click the ticker symbol -> Datatype -> Change and search for the symbol with ticker symbol or name of the company in the search bar as shown: 

Please note that you can identify whether the input stock symbol is valid or not by looking at the icon that appears to the left inside the respective cells as shown here: