Not being able to access your paid content is frustrating but let's see if we can get to the bottom of this for you.
To watch MLB.TV games on Roku device, you must first be an MLB.TV free subscriber, MLB Yearly, Monthly, or Single Team subscriber. In order to access your subscription content on your Roku device, you must visit MLB.TV and enter your MLB.TV subscription information using the virtual keyboard, then click "Log In" to link your account. After this is completed you can access the content that is available for your subscription.
We recommend making sure your MLB.TV account subscription has been linked to your Roku account so you can access your subscription content.
Here is a guide on how to link your subscription: https://www.mlb.com/live-stream-games/help-center/roku-get-started
We hope this information helps. If you have any trouble, let us know by replying to this post or sending us a message directly.