| The invitation link says unavailable | It has been used, or it is more than 14 days old. Ask for a fresh one — links are single-use on purpose. |
| Too many failed sign-ins | Sign-in locks for 15 minutes after repeated failures, counted per address and per network. A shared office connection can lock out an innocent colleague; an admin can clear it. |
| The app says a file is a conflict | Your copy differs from the shared one. Nothing was overwritten. Compare the two, then push the version you want. |
| The project has no model on the site | Nobody has uploaded the drawings yet, or the first build has not finished. An empty project is shown as empty, not as something that failed. |
| The model looks a revision behind | Reload. A page only accepts updates belonging to the model it actually loaded, so it will never quietly show a mixture of two. |