I added a hashed proof in this format in a post: [Verifying my cryptographic key: FINGERPRINT_URI]
and using this claim format for ASP: https://bsky.app/profile/customdomain.com/post/POST_ID
it could not verify it with a tick. I also tried changing the claim format to use my ATProto DID number like this: https://bsky.app/profile/did:plc:12345digitstring67890.com/post/POST_ID
as mentioned in the docs but it also didn't work.
I am doing this on the Android Keyoxide client if it makes any difference. I had to click manual because Bsky wasn't in the list.