Angular Bootstrap UI Datepicker update minDate - angularjs

Question

This should be simple and I believed all my code is correct, but I suppose it is not.
I have two Datepickers. Datepicker 2 should be setting it's minDate to the value of datepicker 1. This works, as I can see the min-date attr updating when I select a date on Datepicker 1, but Datepicker 2 does not re-render the disabled dates. I feel like I should be refreshing the Datepicker somehow, but unsure how.
// Datepicker Controller
app.controller('datepickerController', ['$scope', function($scope) {
// open depart date
$scope.openDepartDatepicker = function($event) {
$event.preventDefault();
$event.stopPropagation();
// open depart datepicker
$scope.departDatepickerOpen = true;
}
// open return date
$scope.openReturnDatepicker = function($event) {
$event.preventDefault();
$event.stopPropagation();
// open return datepicker
$scope.returnDatepickerOpen = true;
}
$scope.$watch('search.searchparams.journeys[0].departuredate',function(value){
$scope.returnMinDate = value;
});
// minDate set intiitally
$scope.departMinDate = new Date();
$scope.returnMinDate = new Date();
// date options
$scope.departDateOptions = {};
$scope.returnDateOptions = {};
// date format
$scope.dateFormat = 'EEE dd/MM/yyyy';
}]);
And here is the actual input
<input id="returnDate" placeholder="Returning" type="text" class="form-control" data-ng-model="search.searchparams.journeys[1].departuredate" datepicker-popup="{{dateFormat}}" data-ng-focus="openReturnDatepicker($event)" show-button-bar="false" min-date="{{returnMinDate}}" is-open="returnDatepickerOpen" datepicker-options="returnDateOptions" readonly=""/>
Nothing I have tried has made a difference. The new minDate is updating, but just not being applied to the Datepicker. I can actually see the updated min-date attribute in my inspector, so all values are updating as expected.
Any help appreciated

Answer 1

The issue is so simple and so silly.
min-date="{{returnMinDate}}"
needs to be
min-date="returnMinDate"
It smacked me right in the face this morning.