Legacy verification does not work

### Steps to reproduce

I need to use legacy verification to verify a bot on one device only, the bot is verified in all of my other sessions but for some reason not this one:

1. Starting in any room with my maubot instance
2. Tap the bot avatar in the page header.
3. Tap the member list.
4. My bot has a red shield in the member list, I tap it.
5. I tap the warning.
6. I tap "not trusted".
7. I tap "manually verify".
8. I tap "use legacy verification".
9. I tap Verify in the lower right and yet...


### Outcome

#### What did you expect?

I expected the bot to be verified and the shield to turn green.

#### What happened instead?

Nothing.

### Your phone model

iPhone 13 mini

### Operating system version

iOS 17.2.1

### Application version

Element 1.11.5

### Homeserver

Synapse 1.98

### Will you send logs?

Yes

Start by reproducing the reported steps on an iPhone 13 mini or comparable iOS device, then inspect the logs promised by the reporter around the legacy verification flow. Confirm the failure at the final Verify action and compare the result with the expected green shield; the issue is done when the bot becomes verified in that session.

Written by the indexing model from the issue text.