I found this thread and read it carefully before venturing inside the sales tax office. However, when I reached the Sales Tax office at beleghata I was taken aback as the entire thing has now been shifted to an online application. I will detail the procedure and how one can get a form 50A (the renamed version from form 50) in a relatively hassle-free way.
Steps:
1. Go to any bank and issue 4 VAT and 4 Entry Tax Challans (costs 6 Rs.) and submit those after filling the form up to the bank. They returned two copies(of each) to me after affixing some stamps to it. Here's how they look.
I had to pay 1% Entry tax on the invoice value (including the 5% VAT already paid there) and 4% VAT (to West Bengal Govt) on the Sale amount that is calculated as "Sale Value = Invoice Value + Freight etc. + 30% profit" (See Note 1).
The User guide can be found in this URL. It's pretty self explanatory.
2. After you have issued the challans, go to this URL: DematWaybillUnregistered.
Enter the details required but make sure that you don't write too much in the address field(see NOTE 2), and submit. On the next web page click on "Dematerialised Waybill Application (Un-Registered)". This is equivalent to the Form 56 which was discussed earlier.
Fill in whatever details you know. In the challan details section, upload the scanned copy of the challan documents (both sides). In my case the challan number was written inside the stamp by the bank official which I had to search for. If you submit it by 3PM, you should receive the password by that day only (as told by a sales tax officer).
3. Once you receive the Password via SMS go back to the last link and select "Generate Dematerialised Waybill (Un-Registered)". You will be able to download the waybill after entering the details, application ID and the password. Just email it to the seller and you're done. Also you may send the credentials to the seller, and he may generate or re-generate the waybill accordingly.
NOTES:
1. The sales tax officer warned me to round up the amount you have to pay to the next digit while submitting the challans. For example Rs. 519.19 becomes Rs. 520.00, otherwise the system will not display this properly and you will have to face a lot of harassment later on.
2. I faced some issues during online application of the waybill, the form ended with no receipt and with some error messages. I had to visit the development team of the web-site in the beleghata office. They told me that the app was developed in a hurry and was not tested for most parts, didn't expect anything better from the govt too. Apparently there was no check in place for the address field for character counts in the text box.
3. I was told by the lady selling the blank challan documents that only the Beleghata branch accepts Entry tax challans. I didn't validate her statement though.
Feel free to update this thread if you find anything useful or if you have any queries, as it will help a lot of other guys.