To check the credential validity of any device please use the "Save & Test" button instead of "Save" button while saving the credential for any device. This will give you a parameter wise report showing which parameters are correct and which ones are wrong for the provided credentials. If you want to test validity for already saved credentials, please open the edit credential slide by clicking the credential icon 
for the said device from device list. Alternatively you can select the device and click on the 3 horizontal dots 
on top right and click on "Apply Credentials". In the edit credential slide please, click on "Save & Test" button to check the validity.
Please note that credential validity can be tested for a single device at a time. If you have selected multiple devices, "Save & Test" option will not be available.