Hello,  I am trying to renew my passport and have completed my application and paid my $130 fee  but cannot purchase a 100 baht Courier Pass Back envelope from the Thailand Postmart System. When I scan the Q code on the application,or follow any of the links on the Bangkok Embassy website  for the  Courier Pass Back I am always directed to the attached a page that shows the 404 error code.  I do seem to able to access other parts of the site and even pay for the same Courier Pass Back but to the Chiang Mai Embassy not Bangkok.  I see that all passport applications in Thailand must go through Bangkok so am afraid that would not work. 

After hours of trying to pay for this service including contacting The Thailand Postmart System and the Thai Post Office no one seems to know anything about it or how to pay for this service. I need to renew my passport and am at my wits end. Is any one else experiencing these problems with the wesite I have attached both the webpages I get when I try to purchase this service. Thank You for any input or help.

Thanks, but after spending about 5 hours working through the broken Thai postal website, written in a foreign language, in order to pay a measly $3 to get my U.S. passport renewal returned to me, I was able to get through the system when it started working again. There has to be a better way.  If I were rating this method of payment, it would be very poor.    Thank You. 

https://www.thailandpostmart.com/product/1013460000929

Found link in FAQ

https://th.usembassy.gov/u-s-citizen-services/passports/faq-on-line-payment/