There is a known issue that forms created with the popular forms plugin “Contact Form 7” are currently not working in popuptexts on layer maps. The shortcode is parsed correctly, anyway due to the architecture of Contact Form 7, the user gets redirected to the GeoJSON output after submissions, where the shortcode is originally parsed. Setting an explicit return url as documented in the Contact Form 7 documentation does not solve this issue.
We have already contacted the developer and asked for a possible fix. In addition we also try to find a fix which can be implemented on our side.
Anyway as we currently have now quick solution in sight, we suggest using an alternative forms plugin, if you need forms in popuptexts on layer maps. For example the also popular and powerful forms framework Ninja Forms is verified to also work on layer maps.