Where are your instructions for authors?

See here:

General Instructions for Authors for all JMIR journals (long form, valid for all JMIR journals)
For journal-specific instructions, follow the "Author Guidelines" link in the footer of each journal homepage, e.g. Author Guidelines for JMIR.
A Word-template of an article compatible with journals from JMIR Publications can be downloaded from https://asset.jmir.pub/assets/public/InstructionsForAuthorsOfJMIR.docx.
Note that the references can be in any format, as long as the in-text citations are sequentially numbered in the manuscript with square brackets and as long as the reference at the end has a PMID in the format PMID:123456. See How should references be formatted?