Following is an extract from the notification received.
Subject to rule 7, a tax invoice referred to in section 31 shall be issued by the registered person containing the following particulars:
(a) name, address and GSTIN of the supplier;
(b) a consecutive serial number not exceeding sixteen characters, in one or multiple series, containing alphabets or numerals or special characters hyphen or dash and slash symbolised as “-” and "/” respectively, and any combination thereof, unique for a financial year;
© date of its issue;
(d) name, address and GSTIN or UIN, if registered, of the recipient;
(e) name and address of the recipient and the address of delivery, along with the name of State and its code, if such recipient is un-registered and where the value of taxable supply is fifty thousand rupees or more;
(f) HSN code of goods or Accounting Code of services;
(g) description of goods or services;
(h) quantity in case of goods and unit or Unique Quantity Code thereof;
(i) total value of supply of goods or services or both;
(j) taxable value of supply of goods or services or both taking into account discount or abatement, if any;
(k) rate of tax (central tax, State tax, integrated tax, Union territory tax or cess);
(l) amount of tax charged in respect of taxable goods or services (central tax, State tax, integrated tax, Union territory tax or cess);
(m) place of supply along with the name of State, in case of a supply in the course of inter-State trade or commerce;
(n) address of delivery where the same is different from the place of supply;
(o) whether the tax is payable on reverse charge basis; and
§ signature or digital signature of the supplier or his authorized representative
While the notification does not refer anything regarding the value in words, it is a common practice in India to mention the value in words. And the sample invoice for GST received from the govt too has the same. So it is like an unwritten rule to have the value in words for elimination errors in accounting and when filing the tax returns.
Regarding the new GST the notification we received is as below. You may go through it if you have some time to spare.