I found a few problems with this issue:

• I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.
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I am using dynamic links to send password reset emails with a custom domain. The generated link in the email looks like this:

https://links.example.com?link=https://example.com/__/auth/action?apiKey%abc%26mode%3DresetPassword%26oobCode%3D9OsQMmdKAPo6J7RRO2bAUMYTV3TEzReToKJpSy-xSWcAAAF2KLCPsw%26continueUrl%3Dhttps://example.com/__/auth/action%26lang%3Den&ibi=com.example.ios&ifl=https://example.com/__/auth/action?apiKey%abc%26mode%3DresetPassword%26oobCode%3D9OsQMmdKAPo6J7RRO2bAUMYTV3TEzReToKJpSy-xSWcAAAF2KLCPsw%26continueUrl%3Dhttps://example.com/__/auth/action%26lang%3Den

The link doesn't have a trailing '/' causing the SDK to fail the customDomainMatchFound check.

I believe the same applies to Google Analytics logging automatically query params.

Universal link https://www.domain.com/someLink?utm_source=email&utm_medium=email&utm_campaign=campaign
doesn't work where
Universal link https://www.domain.com/someLink/?utm_source=email&utm_medium=email&utm_campaign=campaign
does work

@paulb777 Is this intended? If not, should I open another issue, or is it related?

Internal bug created and will be prioritizing and looking into it: b/177469304

Oh man, I've spent days trying to figure out why email sign in links worked fine in Apple Mail but no other email client.

Eventually went deep and logged the incoming url and somehow slash was missing even thought they weren't when manually copied. I assume iOS applies missing slash when copied?.

Anyhow, It's been 2 months since this was filed and is currently breaking email passwordless registrations for iOS users.
So please please, prioritize this some more! <3

For me to get around this issue, I added a temp hack to handleUniversalLink:

- (BOOL)handleUniversalLink:(NSURL *)universalLinkURL
                 completion:(FIRDynamicLinkUniversalLinkHandler)completion {
                   
    NSString *slashedString = [universalLinkURL.absoluteString stringByReplacingOccurrencesOfString:@"ENTER_YOUR_CUSTOM_DOMAIN_HERE?link=" 
      withString:@"ENTER_YOUR_CUSTOM_DOMAIN_HERE/?link="];
    NSURL *fixedUniversalLinkURL = [NSURL URLWithString:slashedString];

  if ([self matchesShortLinkFormat:fixedUniversalLinkURL]) {
    __weak __typeof__(self) weakSelf = self;
    [self resolveShortLink:fixedUniversalLinkURL
                completion:^(NSURL *url, NSError *error) {
                  __typeof__(self) strongSelf = weakSelf;
                  if (strongSelf) {
                    FIRDynamicLink *dynamicLink = [strongSelf dynamicLinkFromCustomSchemeURL:url];
                    dispatch_async(dispatch_get_main_queue(), ^{
                      completion(dynamicLink, error);
                    });
                  } else {
                    completion(nil, nil);
                  }
                }];
    return YES;
  } else {
    [self dynamicLinkFromUniversalLinkURL:fixedUniversalLinkURL completion:completion];
    BOOL canHandleUniversalLink =
        [self canParseUniversalLinkURL:fixedUniversalLinkURL] && fixedUniversalLinkURL.query.length > 0 &&
        FIRDLDictionaryFromQuery(universalLinkURL.query)[kFIRDLParameterLink];
    return canHandleUniversalLink;
  }
}
    ```

I just wanted to add that sign-in links work from other email apps on iOS if a Google-provided domain (e.g. projectname.page.link) is used to generate sign-in links. This can be used as a workaround in some cases.

I have a working example react-native app with a Google-provided domain here.

Can you please fix this???? I've just lost a whole day until I debugged the problem myself and searched for this open issue. This completely blocks custom domains...

I also spent a day trying to find the problem.

https://stackoverflow.com/questions/61393682/firebase-authentication-link-not-working-missing-trailing-slash

@reimertz Hi. I'm having the same problem and I would like to apply your workaround. I've created a local copy of the FirebaseDynamicLinks pod directory, I've modified the handleUniversalLink method and I'm pointing to this local pod inside the main Podfile. Not sure how to write the podspec for the local pod however.

Can you help with some basic steps of using a custom local pod of FirebaseDynamicLinks?

(I'm a Flutter developer so I am not very familiar with how pods work on ios.)

I've also spent the whole day trying to figure out why deep link is not triggered by my app from GMail iOS App.

exactly same^

This seems like purposefully introduced in PR: #2563