Hi,
If you have not created your Azure Cache for Redis, did you first create your Virtual Network as described in article below, in same region (Japan East)?
Create a virtual network for your new cache
If you have already created your Azure Cache for Redis, did you first create your Virtual Network, next navigate to your Azure Cache for Redis -- Private Endpoint blade, click Add Private Endpoint, as described in below article:
Create a private endpoint with an existing Azure Cache for Redis instance
Please note there are small details in above article that are outdated, such as the screenshot showing (PREVIEW), but in general it is correct.
Please click Accept Answer and upvote if the above was helpful. If something is unclear post a comment below and I will assist.
Thanks.
-TP