I didn't previously have an account before ordering my NT Thunder SIM. Just checked now, I used my Covid/Pink ID card number and my Mrs's mobile number to log into my account. The OTP for logging in went to her mobile, of course.
I have a photograph of the QR code activation letter (Steps numbered 1,2,3 & 4).
(Used Google lens to translate from Thai).
Step 1 - Receive and inspect product.
Step 2- Scan QR code and then to fill in; 'Order Number and mobile phone number for the contact specified in the ordering process (not the number of the SIM card received).
Step 3- Enter OTP received.
Step 4- Try it out.
Hope this helps!