When you submit your VAT Return under Making Tax Digital (MTD), you may see the message:

'An error has occurred when communicating with the submission service. Please try again later.'

When you click Details, the following appears:

'Error 403 - The client and/or agent is not authorised.'

HMRC systems can return this error for several reasons, depending on whether you're making your own MTD submission or if you're an agent submitting on behalf of a client.

To correct the error, follow the steps below, but if the issue persists, please contact HMRC for further clarification.

 NOTE: This error also occurs when the wrong period has been selected for submission.

Try logging in again

1. On the error window, click OK, then click Cancel.
2. Click Submit Online and retry the submission, checking your Government Gateway login details are correct.

Things to check for customers and agents

• Make sure you, or if applicable your client, have registered for MTD and actioned the emails received during the registration process. Processing your registration might take up to 72 hours, so make sure enough time has passed
• Check you have enabled MTD in your software. Click Settings then click Company Preferences and click VAT then ensure Enable Making Tax Digital is ticked, then click OK
• Make sure you, or your client, have entered the correct VAT number with no spaces in Sage 50 Accounts. To check this, click Settings, then click Company Preferences. Once checked, click OK
• When completing the MTD VAT submission window, ensure Used stored credentials is not ticked
• Check that your Sage 50 Accounts software is MTD ready, check this now >
• This error can appear at busy times especially near MTD deadlines, so if possible try again later

Additional checks to make if you are submitting for your own company

• When making your submission, ensure that you have entered the correct credentials. Refer back to any emails from HMRC to confirm
• If you have more than one Government Gateway ID, retry your submission with the alternative credentials
• Check that your computer's regional settings are set to English (United Kingdom). To check this, hold down the Windows key  and press R, then type intl.cpl and click OK

Additional checks to make if you're an agent acting on behalf of a client

If you're an accountant using Sage 50 Accounts Client Manager, follow these steps first:

1. Click Settings, then click MTD for VAT Settings...
2. Click Delete Stored credentials.
3. Submit again and when completing the MTD VAT submission window, ensure Used stored credentials is not ticked.

If the problem persists:

• Check that you're entering the correct credentials and attempt the submission again. You must use your Agent Services Account credentials
• Ensure you have created an Agent Services Accounts and assigned your clients
• Ensure you have linked your client to your account. 
• When making your submission, ensure that you have entered the correct credentials. Refer back to any emails from HMRC to confirm
• If you have more than one Government Gateway ID, retry your submission with the alternative credentials
• Check that your computer's regional settings are set to English (United Kingdom). To check this, hold down the Windows key  and press R, then type intl.cpl and click OK

Next steps

If you've completed all of the steps, checked your software is MTD ready, and checked all credentials, then please contact HMRC to find out why they are not accepting your MTD submission.