I have a problem while login to the app as an administrator, when I run my application on Mendix Cloud. I cross Checked with the credentials given in the project as well, but it always says the user or password is invalid.
When running locally, MxAdmin uses the password you specify in your modeler. When running in a different environment, you can set the MxAdmin password in the cloud portal. Source
If you're running a free app, you could consider adding account creation of an admin account to an after startup flow.