Both Sandbox and Production bridging tools require the user to grant the tool authority to access the user's MTD for VAT account.
Make sure your computer has the Internet Explorer browser. HMRC insist that the granting of authority is performed on their web site. So, once you confirm that you wish to authorise our briding tool, you will be taken to the appropriate HMRC web site automatically.
Having already entered your Government Gateway ID and Password into the bridging tool, both will be automatically transferred to HMRC's Sign In page ready for you to commence the authorisation.
The Sandbox bridging tool is demonstrated below:
The Production bridging tool differs only slightly. After Sign In and before you actually Grant Authority, HMRC will send an Access Code to your mobile for you to enter. So keep your mobile to hand.
Once the bridging tool is authorised, you can use the API functionality to exchange information with HMRC. And you only need to grant authority once every 18 months.