DNA Center 2.3.3.7 and On-Prem SSM

[Chris Terry]

I recently got my standalone Cisco DNA appliance up and running. I've been trying to connect it to our On-Prem SSM. I enabled to the API-Console and generated client credentials for the DNAC. When I enter the credentials on DNAC I get the error message "Unable to change mode: clientId or clientSecret are invalid". 

[pieterh]

most of the time it is just as the message says : clientId or clientSecret are invalid

-> double check you did not copied an extra space in one of both fields (use the copy button in the CSSM, not <ctrl+c>)
in addition check version compatibility of DNA vs CSSM version
as the device is recently installed, you may need to wait for the "new version available" message 
or use software management to actively search for the upgrade(s)

also check the logs on the CSSM if this confirms DNA tries to access but is using invalid credentials