I have two queries related to SCRUM. They are as follows:
I have read that the format of SCRUM story is "As a < type of user >, I want < some goal > so that < some reason >". I have to write a story for an API. This API will send an email with a link to validate the email address of the user. What will be the type of user here? Will it be the user logged in?
Do subtasks have story format similar to a story or it can be a normal description?
The trouble you are encountering is likely that you are starting from a determined implementation and then trying to work backwards to the need (unless your product is an API that your users leverage, in which case I think that answers your questions).
When we approach it from a user need, we'll usually end up with more of a problem statement, like
"As a vacationer, I'd like the site to calculate the best route across all types of transportation for me so that I don't have to run many searches to figure it out myself."
One of the pieces of delivering on this need will be creating the API calls if your application architecture calls for that. Then "add API method for aggregated call" may be a task under that user story.
You will have cases where all a particular story needs is API work, and that's fine, but it won't come out in the user story. For example, let's say we did the about user story but limited it to planes and trains for the first start, then we created another story that reads:
"As a vacationer in the US, I want my trip planner to factor in buses so that I can make use of bus tours in my vacation."
Now, maybe the only task in there is to create a some API changes to include the bus routes in the search, but that doesn't cause a problem with your user stories because we started back at the user's problem statement in the beginning instead of starting at the desired implementation and working backward.