addPaste doesn't return api_paste_key, but it's required for getPaste and deletePaste

From the below section - addPaste should also return api_paste_key not just url on success.

We can have SOAP or REST APIs to expose the functionality of our service. Following could be the definitions of the APIs to create/retrieve/delete Pastes:

addPaste(api_dev_key, paste_data, custom_url=None user_name=None, paste_name=None, expire_date=None)

api_dev_key (string): The API developer key of a registered account. This will be used to, among other things, throttle users based on their allocated quota.
paste_data (string): Textual data of the paste.
custom_url (string): Optional custom URL.
user_name (string): Optional user name to be used to generate URL.
paste_name (string): Optional name of the paste
expire_date (string): Optional expiration date for the paste.

Returns: (string)
A successful insertion returns the URL through which the paste can be accessed, otherwise, it will return an error code.

Similarly, we can have Retrieve and Delete Paste APIs:

getPaste(api_dev_key, api_paste_key)

Where “api_paste_key” is a string representing the Paste Key of the paste to be retrieved. This API will return the textual data of the paste.

deletePaste(api_dev_key, api_paste_key)

A successful deletion returns ‘true’, otherwise returns ‘false’.

My understanding is that the url returned is https://<your domain>/paste/<paste key>

Then you just feed <paste key> to your APIs when needed.