After inserting an H5P into Blackboard, the H5P item is not clickable, and the title includes "Invalid Link", like below:
The reason for this is that the domain name defined in the Application (on developer.blackboard.com) is wrong. It shall be <my-subdomain>.h5p.com, where <my-subdomain> means the name you chose when registering the h5p.com account.
To fix this, the Application on developer.blackboard.com has to bed edited, and the correct domain name has to be listed in the Domain(s) field:
When this has been done, you need to recreate the LTI Tool Provider and add the Placement once more. The existing LTI Tool Provider can be removed.
When this has been done, the inserted H5P Item will be clickable, and it no longer has the "Invalid Link". But, when clicking it, you will see something like the below:
It seems Blackboard is keeping a reference to the Tool Provider in the database, and therefore the H5P item needs to be reinserted. The existing one(s) can then be deleted.
Note: there is a "Synchronize LTI 1.3 tools" feature on Blackboard. During our testing, this does not seem to help in any way for this scenario