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 clicking on the Test Sign On button
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.
The automated Gift Aid Claims process is available with Starter, Professional and Enterprise plans. Essential subscribers, please contact us to find out more about upgrading.