Headings clarify your logic and organization for the reader by establishing a hierarchy of sections in the paper. If you have a subheading under a larger heading, there must be more than one subheading nested under that larger heading. For instance, if you have a Level 1 heading and you want a subheading below it, there needs to be more than one Level 2 heading under the Level 1 heading.
Also, note that title case means only the first letters of words with four or more letters are capitalized, while all other letters are left lower case. Sentence case means that only the first word of a title is capitalized, while all other letters are left lower case.
APA style allows five different heading levels. In a Walden doctoral capstone study or project, there is an additional Walden heading level, Level 0. In a doctoral capstone study or project, there are typically three or four heading levels: L0, L1, L2, and, if needed, L3 and L4.
Use a Level 0 heading (or title heading) formatting for the References heading of your reference list as well as for any appendices. The capstone document templates are also formatted with correct APA headings.
(Note that Level 3 and Level 4 APA headings have changed from APA 6. The examples here are from APA 7.)
Additionally, all of the templates are formatted with correct APA headings.
For more information on headings in Walden capstone documents, see the SMRTguides Creating a Literature Review Outline and Correcting Common Errors in the Template Table of Contents.