'The data you sent could not be processed.' error

Hi !

I'm tryng to create a connector, but when I try to get an access token I get this error message :
{ '$severity': 'error',
'$dataCode': 'DataParsingError',
'$message': 'The data you sent could not be processed.',
'$source': 'Proxy' }

Did someone already encounter this message and know how to solve it ?

Aladin.