Make sure you select the "Microsoft Login" option (instead of "Mojang Login") and request a password reset for your Microsoft account if you're not having any luck. ^NS
First, please have your friend double check that they're logged in with the same account that purchased the Realm. If you can confirm it's the same account, then go ahead and contact us at msft.it/6013ZngnR and our Realms team will look into that for you. ^NS
Reselling a code does violate our Terms and Conditions. If your purchase was through a reseller website, unfortunately we won't have a record of it and can't provide support if you lose access. We have a bit more information here msft.it/6010ZngJK if you need! ^NS
Since we didn't create this Marketplace content, unfortunately we can't assist with this issue. Please contact the Marketplace partner who owns that pack to get support. Search for the pack item, click "See More by: Author Name” then click “Get in touch." ^NS
It sounds like this is an error related to the Windows Store. Please try contacting Microsoft Support at msft.it/6010Zn5DY, and be sure to include your error message. ^NS
If you're not receiving password reset emails, please try requesting them from a different browser and checking your junk/spam folder. Also, make sure your email is not blocking or filtering emails from noreply@mojang.com. ^NS
New Java accounts use the security functions of Microsoft accounts. Unfortunately we're not able to make changes to this, but please see msft.it/6013ZneUv for helpful information about setting up a new child account. ^NS
Unfortunately we're not able to assist with third party launchers or clients as they are not run by us. For more information, please visit our FAQ msft.it/6014ZndCk the application's developer. ^NS