Yathit Mobile App, as well as Chrome Extension, use SugarCRM REST API. If Yathit mobile could not login, it is very likely that your CRM may have issue serving REST API. Serving REST API requires additional PHP modules, which is not require just for serving Sugar web portal. It is also possible PHP error and warning message are messing up in REST API output.
To check it, use the following REST login as bash shell.
url=https://demo.suiteondemand.com
username=max
passhash=$(md5 -q -s max)
body="method=login&input_type=JSON&response_type=JSON&rest_data=%7B%22user_auth%22%3A%7B%22user_name%22%3A%22$username%22%2C%22password%22%3A%22$passhash%22%7D%2C%22application_name%22%3A%22Yathit%20test%22%2C%22name_value_list%22%3A%7B%22language%22%3A%22en_us%22%2C%22notifyonsave%22%3A%22false%22%7D%7D"
curl "$url/service/v4_1/rest.php" -H 'Pragma: no-cache' -H 'Content-Type: application/x-www-form-urlencoded' --data $body
Above command will produce the following output:
{"id":"ad987283f667154380b15d4195335a01","module_name":"Users","name_value_list":{"user_id":{"name":"user_id","value":"seed_max_id"},"user_name":{"name":"user_name","value":"max"},"user_language":{"name":"user_language","value":"en_us"},"user_currency_id":{"name":"user_currency_id","value":""},"user_is_admin":{"name":"user_is_admin","value":false},"user_default_team_id":{"name":"user_default_team_id","value":null},"user_default_dateformat":{"name":"user_default_dateformat","value":"m\/d\/Y"},"user_default_timeformat":{"name":"user_default_timeformat","value":"H:i"},"user_number_seperator":{"name":"user_number_seperator","value":","},"user_decimal_seperator":{"name":"user_decimal_seperator","value":"."},"mobile_max_list_entries":{"name":"mobile_max_list_entries","value":null},"mobile_max_subpanel_entries":{"name":"mobile_max_subpanel_entries","value":null},"user_currency_name":{"name":"user_currency_name","value":"US Dollar"}}}
Where you will substitute url, username and password to test in your CRM credentail. In the above username is 'max' and password is 'max'. If it output similar, your REST API login is working.