Getting error in in-app purchase "No product found or product is invalid" in ios

Hello,

I’ve integrated in-app purchase(sandbox mode) in my application. The first time when i’ve checked it, it was working fine and I was getting that product whenever I was fetching it and also was able to purchase it. But from some days I am not getting any product whenever I am fetching it. I’ve upgraded my developer account before some days. Also I’ve not changed anything in my code regarding this.

Also, I have deleted my previous products and added new ones. These are also giving the same problem.

Also I’ve checked bundle identifier, provisioning profile and certificates.

Sometimes I am also getting the error “The item you tried to buy is no longer available”

Please help me to find out where I am missing any step.

Thanks in advance.