Hi Geovany,
» "Change your own password" options are enabled, but when I do so it shows me the same message as when I want to log in from the mobile app: "Invalid login, please try again."
Based on the information provided, it appears that the issue is not directly related to the app. (I noticed that you have already posted on the Authentication forum.) Please revise the the Authentication configuration of your Moodle LMS.
Regarding the app, I would like to add that if your Moodle site uses a SSO auth method (Shibboleth, CAS, Google OAuth, etc), then you need to change the configuration for 'Type of login' (typeoflogin) in 'Mobile authentication' in the Site administration to via a browser window or via an embedded browser. (Please visit Moodle app guide for admins: SSO authentication method as well as Moodle app FAQ - My Moodle site uses a SSO auth method (Shibboleth, CAS, Google OAuth, etc) and the app is not working and Moodle app FAQ - SSO is not working with my custom auth plugin)
Kind regards,
Isabel