Hiroyuki Kikuchi Greetings!
Could you tell me the cause of this issue??
As Dillion mentioned, Fine tuning is currently not available for new customers as it is turned off for all regions. If you have previously fine-tuned & deployed in a region, then you can fine tune in that region if it's available.
This is due to the demand of the service causing capacity constraints.
Unfortunately, we don't have any ETA at this moment when fine tuning opens again.

The models page will be updated as soon as we open up regions for fine tuning and users should be able to submit requests when it is made available.
I hope this helps! Do let us know if there are any further queries.
If this answers your query, do click Accept Answer
and Yes
for was this answer helpful. And, if you have any further query do let us know.