How do I resolve this include-media error.

Error: Undefined mixin 'media'.
        on line 749 of /Volumes/current/Current/Projects/h5bp-bootstrap4-master/_scss/_project.scss, in `media'
        from line 749 of /Volumes/current/Current/Projects/h5bp-bootstrap4-master/_scss/_project.scss
        from line 60 of /Volumes/current/Current/Projects/h5bp-bootstrap4-master/_scss/__main.scss
  Use --trace for backtrace.

code]
$grid-breakpoints: (
  xs: 0,
  sm: 576px,
  md: 768px,
  lg: 992px,
  xl: 1200px
)
!default;
@include _assert-ascending($grid-breakpoints, "$grid-breakpoints");
@include _assert-starts-at-zero($grid-breakpoints);

$breakpoints: $grid-breakpoints;      //include-media expects $breakpoints
[/code]

/* Extra Small Devices, Phones */
@include media(">xs") {                                   //This is Line 749 which returns the error
   .navbar-header-iPhone {
      border-top: solid .2rem red;
    }
}