When putting a doi on the end of the reference, are you meant to include the https part or just the numbers?

For APA 6th edition, you have 3 options for representing DOIs - see the DOI box on the page linked below for each of the variations.

Https is one of the options, just doi:xxx is another. You can choose either (or the http version, however this is less used), but you should be consistent and use the same format for all your references in your assignment.

For your information, when we move to APA 7th edition in July 2020, the format for DOIs will be https ONLY.