AppwriteException: document_invalid_structure, Invalid document structure: Missing required attribut

I was trying to make a chat app and encountered this error when I tried to use Server API to progmatically create collection
if (collection.attributes.isEmpty) {
await _defineDocument(collection.$id);
}
// Return the collection id
return collection.$id;
}
Future _defineDocument(String collectionId) async {
// Defining attributes
try {
// You are free to choose your own key name.
// But make to sure to replace those things in the model too.
await database.createStringAttribute(
databaseId: AppwriteConstants.databaseId,
collectionId: collectionId,
key: "sender_name",
size: 255,
xrequired: true);
wrote similar code for other attributes as well

When I go to appwrite console, it does show that these attributes are created...but gives the error that the required attribute is missing (with the same name as you can see)
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: AppwriteException: document_invalid_structure, Invalid document structure: Missing required attribute "sender_name" (400)

if anyone's reading this pls try and help, i been stuck here for a lot of days

Does this error occur when you try to add a document to the collection that is shown in the screenshot above? Or just by running the above code?