I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this!
Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer. Accepted answers show up at the top, resulting in improved discoverability for others.
Issue: I am trying to run stored procedure from Azure Portal UI. The container has hierarchical partition with two levels. When trying to give the partition key value im providing input as json: {"level1": "value1", "level2": "value2"} This is leading to bad request, could anyone please suggest how to do it correctly
Solution: I was able to figure out how to send hierarchical partition keys in stored proc using Azure portal. This is what worked for me: ["level1_value", "level2_value"]