What am I doing wrong with the Pocket API for Objective-C that's causing archive commands to fail?

I'm really scratching my head at this one. I'm using the Pocket API to allow users to archive Pocket articles from my app, but whenever I try to do so with the below code I get this error:

Error Domain=PocketSDK Code=400 "Invalid request, please refer to API documentation" UserInfo=0xc17d3b0 {NSLocalizedDescription=Invalid request, please refer to API documentation}

Code:

NSDictionary *arguments = @{@"action": @"archive",
                                     @"item_id": articleID};

[[PocketAPI sharedAPI] callAPIMethod:@"send" withHTTPMethod:PocketAPIHTTPMethodPOST arguments:arguments handler:^(PocketAPI *api, NSString *apiMethod, NSDictionary *response, NSError *error) {
    if (!error) {
         NSLog(@"Archived article.");
    }
}];

Exactly what part of that is incorrect? Am I not POSTing a send method to the API?

EDIT: I even changed it to have @"action" be @"actions" and to supply it the above NSDictionary, and it returns without an error but doesn't affect it on the Pocket website...

EDIT 2: Per the response of Joseph Chen I changed my code to the following:

  // Create data to pass to the Pocket API (a JSON array of actions)
  NSError *error;
  NSArray *actions = @[@{@"action": @"archive",
                                @"item_id": articleID}];
  NSData *actionsAsJSONData = [NSJSONSerialization dataWithJSONObject:actions options:kNilOptions error:&error];
  NSString *actionsAsJSONString = [[NSString alloc] initWithData:actionsAsJSONData encoding:NSUTF8StringEncoding];
  
  NSDictionary *arguments = @{@"actions": actionsAsJSONString};
  
  [[PocketAPI sharedAPI] callAPIMethod:@"send" withHTTPMethod:PocketAPIHTTPMethodPOST arguments:arguments handler:^(PocketAPI *api, NSString *apiMethod, NSDictionary *response, NSError *error) {
        if (!error) {
             NSLog(@"%@", response);
        }
        else {
             NSLog(@"%@", error);
        }
  }];

Which returns:

action_results" =     (
    1
);
status = 1;

Yet when I go to the web site and log in, the article I "archived" is still staring me in the face, un-archived.

Here's the code taken (almost) straight from my app:

NSTimeInterval timestamp = [[NSDate date] timeIntervalSince1970];
NSDictionary *arguments = @{@"actions" : @[@{@"action" : @"archive",
                                             @"item_id" : itemId,
                                             @"time" : [NSString stringWithFormat:@"%ld", (long)timestamp]}]};

[self.pocketAPI callAPIMethod:@"send"
               withHTTPMethod:PocketAPIHTTPMethodPOST
                    arguments:arguments
                      handler:^(PocketAPI *api, NSString *apiMethod, NSDictionary *response, NSError *error)
 {
     if (!error) {
         // OK
     } else {
         // handle error
     }
 }];