I recently purchased synplant from plugins boutique and followed all instructions to install and register. But when I enter the serial number given to me with my purchase, it says that it is invalid. , need help please. thank you.

Hi, did you do step B here?
https://soniccharge.com/forum/topic/395-register-your-serial-number-redemption-code

yes I did but had problems with the product registration page when I added the serial number, it saying invalid.

I just retried again to see if it would work this time but this message pops up in red letters. "Invalid redemption code, please try again"

Oh, not good, I'll contact you directly so we can continue in a private conversation and take a look at that redemption code.