Hi Srinivasulu Valleti •,
Welcome to Microsoft Q&A forum.
As I understand, you are getting error when creating new item in Cosmos DB as PartitionKey extracted from document doesn't match the one specified in the header.
When creating a new container make sure use "/" before the key name.
Also, make sure to pass the value of partition key instead of name of partition key.
Refer to the similar post with solutions which might help in your case: https://stackoverflow.com/questions/58121736/partitionkey-extracted-from-document-doesnt-match-the-one-specified-in-the-head
Let us know if this helped.
Thanks