Check your spam/junk folder and/or search your email for "Roku". If you don't get an error message then the process at least thinks there's nothing wrong with the sent email. If you still can't find it then perhaps @RokuMary-F can help.
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As mentioned by @renojim, kindly check for the email on your spam or junk folder if it's not in the inbox. If this issue is not resolved, please let us know along with any additional information you may have that would be helpful for our team to assist you further in this activation problem. Please include the serial number/device ID of your Roku device.
Keep us posted and we'll continue assisting from there if needed.