Add equals as permitted URI character (#4329)

This should resolve the 400 error when deleting payments with base64 encoded IDs containing `=`.

app/Config/App.php

@@ -117,7 +117,7 @@ class App extends BaseConfig
     | DO NOT CHANGE THIS UNLESS YOU FULLY UNDERSTAND THE REPERCUSSIONS!!
     |
     */
-    public string $permittedURIChars = 'a-z 0-9~%.:_\-';
+    public string $permittedURIChars = 'a-z 0-9~%.:_\-=';
 
     /**
      * --------------------------------------------------------------------------