I'm confused by your statement of "combine shipping"
I did a sample product with a flat rate shipping of $5 and a 2nd of USPS
If I have just the USPS $20.90 - If I add the product with flat rate it's $25.90 so this is working as I would expect.
I am a GoDaddy End User - Just Like You Check out my site! | I currently manage over 300 WordPress Websites * Please note that I offer free advice on this forum. Thank You Info If you would like personalized help, please contact me. Otherwise, please ask your question in the proper forum so the answer can assist EVERYONE in the community and not just you. Thanks! *
Once your issue is resolved, please be sure to come back and click accept for the solution