Which Forms version are you running? (see apps page)
1.1.1
Nextcloud or ownCloud?:
Nextcloud
Nextcloud/ownCloud version: (see Nextcloud admin page)
18.0.2
Error interno del servidor
El servidor no pudo completar tu solicitud.
Si esto vuelve a suceder, por favor envia los detalles tecnicos siguientes al adminsitrador del sistema.
Puedes consultar m谩s detalles en la bit谩cora del servidor.
Detalles t茅cnicos
Direcci贸n Remota: XX.XX.XX.XX
ID de solicitud: MhKx99S74lWaJjuMoPAN
Be able to see and fill the public form

Could this be a duplicate of #178?
Looks like is probably the same, but i dont find the file PageController.php that is mentioned on the fix.
What does your log say?
On the NC admin Panel.
Error | index | Exception:聽Argument 2 passed to OCAFormsDbNotificationMapper::findByUserAndForm() must be of the type string, null given, called in /var/www/nextcloud/apps/forms/lib/Controller/PageController.php on line 277
-- | -- | --
So with the log in the admin panel i found the location to apply de patch on #178
after that i did:
cd /var/www/nextcloud/apps/forms/lib/Controller/
cp PageController.php PageController.backup.php
wget https://github.com/nextcloud/forms/files/4091661/PageController_notifMapper_patch.txt
patch < PageController_notifMapper_patch.txt
That fix the problem, thank you @dwaxweiler
I am happy to hear that! I hope a new release with this bugfix will follow soon too. :)
Most helpful comment
So with the log in the admin panel i found the location to apply de patch on #178
after that i did:
cd /var/www/nextcloud/apps/forms/lib/Controller/
cp PageController.php PageController.backup.php
wget https://github.com/nextcloud/forms/files/4091661/PageController_notifMapper_patch.txt
patch < PageController_notifMapper_patch.txt
That fix the problem, thank you @dwaxweiler