How to treat missing requirements

@Yassiel Oliva, Do what is necessary to make the situation transparent and to get the work to a "Done" state.

I know you're asking for some instruction on which option is best to take and what do next, and I will provide you suggestions...but first remember that's not exactly Scrum. Those decisions/changes will come from the Scrum Team through Inspect and Adapt.

Scrum doesn't outline how to handle this specifically because Scrum is a framework for your processes, and Scrum will help you identify problems within the existing processes and put the responsibility of making those improvements onto the Scrum Team.

Now for the suggestions...

The Sprint has helped you identify there is a process gap somewhere. Retrospectives give the team opportunities to solve their own problems and experiment with solutions. Some questions to consider asking:

• How did this situation get identified?
• Why so late in the process/workflow?
• What action can we take next sprint to improve and prevent situations like this?
• If this does happen again, how do you (the Dev team) want to handle this?
• Should the Working Agreement be updated for this change? 

I recommend first creating the bug and then assess the current Story.

• As a customer/stakeholder of the team, should this functionality and Sprint Goal be demoed to me and called complete?
• If no, then it's a good idea to resolve this bug in current Sprint. I don't see the need to create a separate story in addition to this bug.
• Can the Story be considered "Done" based on existing Definition of Done?
• Should the DoD be updated because team realizes this work should not be called "Done"?

Any issue preventing work to be called "Done" is a development bug, even if the resolution of it doesn't go directly to a developer. The team needs to be cross-functional and so the resolution shouldn't be dependent on someone who isn't a part of the team. If they do, and especially often, then the structure of the team should be assessed by the Scrum Team.

the QA detects a missing requirement in the initial specification of the ticket. how we should handle this case according to Scrum?

Does the team consider the requirement to be essential to the Sprint Goal? .find_in_page{background-color:#ffff00 !important;padding:0px;margin:0px;overflow:visible !important;}.findysel{background-color:#ff9632 !important;padding:0px;margin:0px;overflow:visible !important;}