Trouble creating a new record in Rails with Select Boxes and Foreign Keys

Ruby on Rails newbie here.

TL;DR: When trying to create a new record, I get an error message saying my foreign keys must exist. I'm using Select Boxes on my view. Need help.

I am creating a requests management system for our own support staff here in our company. So far, I have generated a scaffold for Issues and 2 models, one for Category and another for Subcategory.

So far, the relationship I came up with is designed like this:

Issue belongs to Category and Subcategory Subcategory belongs to Category.

This means that a user may have a problem with his keyboard, for which he will create an Issue. This issues would belong the the subcategory named "Peripherals", which would in turn, belongs to a broader "Hardware" category.

I still need to implement Ajax to fetch data for my Select Boxes, but while testing it out in a simpler scenario, I couldn't create my Issues from the "New Issue" view. I come across an error message saying that Category and Subcategory must exist. I've reviewed what I've written so far, but couldn't find my mistake.

Here is the code for my create method in the Issues controller

def create
  @issue = Issue.new(issue_params)

  respond_to do |format|
    if @issue.save
      format.html { redirect_to root_path, notice: 'Issue was successfully created.' }        
    else
      @categories = Category.enabled
      @subcategories = Subcategory.enabled
      format.html { render :new }        
    end
  end
end

Here go my Models

Issue Model:

class Issue < ApplicationRecord
  belongs_to :category
  belongs_to :subcategory
end

Category Model:

class Category < ApplicationRecord
  has_many :subcategories
  has_many :issues

    enum status: { disabled: 0, enabled: 1 }

    after_initialize :set_defaults

  def self.enabled
    where(status: 'enabled')
  end

    def set_defaults
        self.status ||= 1
    end
end

Subcategory Model

class Subcategory < ApplicationRecord
  belongs_to :category
  has_many :issues

  enum status: { disabled: 0, enabled: 1 } 

  def self.enabled
    where(status: 'enabled')
  end

  after_initialize :set_defaults

  def set_defaults
    self.status ||= 1 
  end
end

And finally, here are the parameters passed to the controller:

Processing by IssuesController#create as HTML
Parameters: {"utf8"=>"✓",  "authenticity_token"=>"tzKDayYfEbEwTaOFup/N9kQ+8tr9c0P5otV2B0boKGrgyv+HkQaEvYJ6ZMQeR+8XgCnhJR6PosVcx0jPJpqBEA==", "category_id"=>"1", "subcategory_id"=>"1", "issue"=>{"description"=>"Replace broken keyboard.", "status"=>"1", "criticality_level"=>"1"}, "commit"=>"Create Issue"}

I was able to create an Issue via Rails Console, though.

Could anyone give me a hint on how to solve this? Thanks guys!

modify create action as follows

def create
  @category = Category.find(params[:category_id])

  @issue = @category.issues.build(issue_params)

  respond_to do |format|
    if @issue.save
      format.html { redirect_to root_path, notice: 'Issue was successfully created.' }        
    else
      @categories = Category.enabled
      @subcategories = Subcategory.enabled
      format.html { render :new }        
    end
  end
end