Hi @vanitharaj1208 ,
I had also created a playbook to convert json to csv and attaching csv file to case wall as below:
1. Used 'CSV - Save Json To CSV' to get the json object in csv file. This action is available in CSV integration from marketplace.
2. Used 'FileUtilities - Get Files as Base64' action to convert this csv file to base64 strings.
3. Used 'FileUtilities - Add Attachment' action and provided base64 blob of 'FileUtilities - Get Files as Base64 json results' and in Type provided .csv file type to attach csv file to case wall.