Thank you for your post.
Our Development and Testing departments are aware of this issue, as it has occurred since FileMaker Server 13.0v5. This was changed due to a Security issue. Investigation on how to embed the iframe is ongoing.
It will work in Web Direct because you are now working with a browser (not FileMaker Pro) accessing the database file.
I have attached your post to the original report. When more information becomes available, I will post again.
This issue appears to have been addressed in FileMaker Server 14.0.4.
FMS v14.0.4 does not address this issue. The release notes said "For FileMaker WebDirect and Custom Web Publishing content to display in
<iframe>tags of separate webpages, those webpages must also be hosted by the FileMaker Server web server. Webpages hosted by other web servers cannot use the
<iframe>tag to embed FileMaker WebDirect and Custom Web Publishing content."
That is different than the problem I described. The Google Maps Embed API continues to generate an error when viewed in a database run with FMS 14.0.4 and viewed in a FM 14.0.4 client but works fine when viewed in WebDirect. There has been no change in behavior on this issue since at least 14.0.1 for both clients and server versions.
The problem is illegal use of API, not bug of FM.
You need the URL is in src of <iframe>, as the error message says. You can't open the URL not only in web viewer in FM, also any web browser (don't mean WebDirect, opening the URL itself in browser).
(You seems using undocumented parameter svembedmfe, Google might change the behavior)
Try something like
"data:text/html,<iframe style='width:100%;height:100%' src='" &
"https://maps.google.com/maps?t=h&output=svembedmfe&iwloc=0&" & "q=" & COUNTRY FIELD & ", " & CITY FIELD
This will not work on WEBD, use Case() function if you need to work on both.