Thank you for your question and picture for Extension. It looks like you bought a raspberry plant. I'm not sure exactly why it's dying without more information. Did you recently buy it? Is there a warranty or return policy where you bought it? I think it needs to be planted as soon as possible as it may be root bound. It's best not to plant on a very hot day, but if you do, be sure to plants it in the depth it is in the pot. Here is an article from Extension about raspberries:

Growing raspberries in the home garden | UMN Extension

As you will see, it does say to prune your raspberries annually. Also, you can check out some pictures of why your plant is not thriving.

I realized after I sent this that you identified your plant as a blackberry and I answered your question with raspberry information. The care and information of blackberries would be similar to what I sent you about raspberries. Here is some good information about growing blackberries:

How to Grow and Care for Blackberries (thespruce.com)

Let me know if you need further information or have questions.