If you have completed your gift aid settings - using the Settings tab under Financial | Gift Aid - you can check your sign on details are valid by making sure 'Submit Gift Aid Claims to Live Gateway' is set to yes - as shown below
Next click on the Previous Claims tab - and press the Retrieve Status Updates from HMRC - if you see an error message as shown below in the example below then there is a problem with your settings - most likely the Sender Id and / or Sender Password are not valid - note that you also need 'Charities Online' added to your HMRC account - see this page https://www.gov.uk/claim-
You can try signing into the HMRC services directly to check your Id and Password.
If you do not see an error then your Sender Id and Sender Password are valid. Note the retrieve status updates can only check for claims submitted by Donorfy - i.e. details of claims you have submitted by other means cannot be retrieved.