This is usually the result when ~redeem~ in the reward message is aligned with a period (see image below). 

 

Some devices read the [ . ] as an extension of the URL and will not open the page, resulting in a 404 error.

Any time ~redeem~ is the end of a sentence, either don't include a  [ . ] or make sure that there is a space between the last ~ and the period (ex: ~redeem~ . ).