Domain verification failed. and target domain is not same as OAuth redirect url

We are currently planning to submit an update for review for our currently released app ‘Narrative Phone’.
We are at the stage of domain verification, but it is not being verified.
The domain for the app’s support and other pages is ‘phone.narrativebook.jp’, and the last time we reviewed it, it was verified by placing an HTML file in the root directory, but this time the method has changed, and the target domain is now ‘narrativebook.jp’.
‘narrativebook.jp’ is used by our another app, ‘NarrativeBook’.
I tried adding a TXT record to DNS, but that didn’t work, so I tried uploading an HTML file, but the .html file that was downloaded was a 0KB file.
I placed this in the root directory of narrativebook.jp, but it did not pass verification.
Please tell me how to verify the domain.