I have come up with the simplest procedure to change Mobile Number or Email ID on GST portal. Just follow the below mentioned steps:
1. Login to your account
2. Go to SERVICES-> REGISTRATION- > ADMENDMENT OF REGISTRATION NON-CORE FIELDS
Note : If you are unable to edit anything then go to Services-> My Saved Application. Then click on Edit.
3. Go to Authorized Signatory Tab and click on ADD NEW
4. Add a Dummy Person (Designation-authorized signatory) details just like you filed for Proprietor. Upload documents as well. Enter the MOBILE NUMBER and EMAIL ID you want to update on GST portal and click on SAVE.
5. You can see dummy person is also added.
6. Now click on Edit -original authorized signatory(proprietor) and Uncheck the Primary Authorized Signatory Box. Uncheck that Right Mark in the Square Box.
7. Now go to the dummy person (authorized signatory) and click on Primary authorized signatory box. It should turn green with right mark.
8. When you click on check box. You can see in the Mobile No. and Email ID tab it shows the previous Mobile No. and Email ID.
9. Here the main step comes.
Note: Don't forget to change the mobile number or email id which you want to update.
10. Once it is done click on Save. When you click on Save there appears a Pop up window where it ask you to enter the OTP which you received on New Mobile No. and Email ID.
11. Enter the OTP and it verifies.
12. Once its verifies your new Mobile Number and Email id is updated.
13. Now again uncheck the primary authorized signatory tab in dummy person(authorized signatory). And DELETE the dummy person(authorized signatory).
NOTE: Before you submit you application Don't forget to delete the dummy person(authorized signatory).
14. Then go to Proprietor tab and click on Primary authorized signatory tab. You will see new mobile number and email id. Click on SAVE and CONTINUE and Submit your application.
Hurray finally your mobile number and email id is updated.
Also, read how to fix failure in establishing a connection with the server on GST Portal.