This issue probably happens because you are the using the client key and the server key of the Web api not the Mobile SDK, so you need to contact customer care to get your mobile keys.
This issue most often because you are using invalid server key, client key, profile id or merchant country code Please check them all with the customer care to validate they are correct values.
This happens due to some semantic validation error, it often occurs because of the wrong currency. Please check with customer care to validate the correct value.
This is a general error message, please send your credentials to customer care, and ask them about the issue.