###

### Steps to reproduce

1. Login and Begin of the insertionmake sure webp images are not supported on your instance (example here: https://qa.openproject-edge.com/admin/settings/attachments)

2. OpenEnd of the insertion Begin of the deletion openEnd of the deletion a work package

Begin of the insertion3.End of the insertion Begin of the deletion 2.End of the deletion In the description, try uploading a webp image


### What is the buggy behavior?

Begin of the insertionThereEnd of the insertion Begin of the deletion Impossible to proceed as thereEnd of the deletion is Begin of the insertiona ckeditorEnd of the insertion Begin of the deletion anEnd of the deletion error Begin of the insertionbut it's not clear enough for the user.End of the insertion Begin of the deletion (visible on ui and in console)End of the deletion

<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/919092/content">

### What is the expected behavior?

1. Begin of the insertionThereEnd of the insertion Begin of the deletion WeEnd of the deletion should be Begin of the deletion able to uploadEnd of the deletion a Begin of the insertionspecific and clear error message informing users that this type of file is unsupported.End of the insertion Begin of the deletion webp image.End of the deletion


###

### Environment information

**OpenProject version**

**Core build**

[803f5e5adbc2e948a119285edd41281f7ece9d15](https://qa.openproject-edge.com/external_redirect?url=https%3A%2F%2Fgithub.com%2Fopf%2Fopenproject%2Fcommits%2F803f5e5adbc2e948a119285edd41281f7ece9d15)

**Product version**

[83768de97a9b536b5b2d7a0fe516e5442c46bf2e](https://qa.openproject-edge.com/external_redirect?url=https%3A%2F%2Fgithub.com%2Fopf%2Fsaas-openproject%2Fcommits%2F83768de97a9b536b5b2d7a0fe516e5442c46bf2e)

**Core version**

OpenProject 17.2.0