1-Incase PAN details invalid, Go to "Searchpan", enter your pan number there, and it will show you your actual name existing on the PAN database, Very often due to Long names everyone dont get there Full name on the PAN card, but it is there on the database, GST website tried to match PAN details as per CB database and not how its shown on the PAN card.
2-Incase application for applying GSTN is rejected (Usually happens when the officer is not convinced with the data provided OR queries werent cleared by the assesse within the said period, i.e. 7 days), you need to apply for a fresh registration.
Note:- Combination of PAN, Contact number and email cannot be same for different businesses or GSTN.ie, we cannot have all the 3 things same for other registration also, either of the 3 should be different.
3- You can apply for as many GSTN you want with the same PAN, (Common sense, an individual can have different/multiple business but only one PAN)
4- Incase your CA isnt giving you the username and password then no worries, You can know your username by selecting "Forgot username", which will ask you to enter GSTN, provisional number, etc and u will get OTPs on the email id and phone number provided on the Portal (USERNAME will be mailed and texted as well on the same details email id and number). Once u get to know your username then do "Forgot Password" and reset it, again the OTPs will be sent on email Id and contact number, change the password then.
Note:- OTPs either of email ID and number provided are to be entered, not of both
AN ADVICE FOR ALL: KINDLY ENTER THE EMAIL ID & CONTACT NUMBER USED BY YOU & WHICH ARE ACTIVE, ITS ALL ABOUT EMAIL ID & CONTACT NUMBERS ON WHICH THE OTP ARE SENT, "YOU CANT CHANGE THE NUMBER AND EMAIL ID ON WHICH THE OTP IS SENT ONCE REGISTERED)".