Hi @Omar José Tercero Moreira ,
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer.
Issue:
When attempting to reach the sandbox, you received the message, "The client 'live.com#xxxxxx@xxxxx.com' with object id 'exxx12dx-4xxx79xxxf2-22339xxxxx49f' does not have authorization to perform action 'Microsoft.Storage/storageAccounts/read' over scope."
Then, in the AZ-104 Unit 4/7, you were following the steps to use a shared access signatures to delegate access to Azure Storage, but you were unable to pass the image verification steps.
Solution:
You needed to do 10/10 with the verification account in order to pass it and reach the sandbox, and everything is working now.
If you have any other questions or are still running into more issues, please let me know. Thank you again for your time and patience throughout this issue.
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.