Only validate lower case servernames #11

The spec allows but discourages upper case servernames
https://spec.matrix.org/v1.2/appendices/#server-name
Furthermore, server names are case sensitive for some reason

CHANGELOG.md

@@ -9,6 +9,10 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Changed
+
+- Allow lowercase server names only #11
+
 ## [1.3.0] - 2022-04-19
 
 ### Added

pretix_matrix_inviter/signals.py

@@ -46,7 +46,7 @@ def add_matrix_id_question(sender, position, **kwargs):
         "matrix_inviter_matrix_id": forms.RegexField(
             label=_("Matrix ID"),
             required=False,
-            regex="@[a-z0-9._=/-]+:.+",
+            regex="@[a-z0-9._=/-]+:[a-z0-9.-]+",
             strip=True,
             error_messages={
                 "invalid": _("Enter a Matrix ID of the form @username:homeserver.tld")