Can't deploy SageMaker Application. Claims my quota is "0" with an error message every time I try, yet my quota shows as 30 when I check it.

This situation you're experiencing is unusual and seems to be a discrepancy between the actual quota and what the SageMaker service is recognizing. Here are a few steps you can take to troubleshoot and potentially resolve this issue:

1. Double-check the AWS region: Ensure that you're checking the quota and trying to create the SageMaker App in the same AWS region. Quotas can vary between regions.

2. Verify the specific quota: Make sure you're looking at the correct quota for "Studio Jupyter Apps running on ml.c5.large instances" in the Service Quotas console.

3. Refresh your session: Try logging out of the AWS console completely, clearing your browser cache, and logging back in. Sometimes, cached information can cause discrepancies.

4. Use AWS CLI: Try to create the App using the AWS Command Line Interface. This might provide more detailed error information.

5. Check for any pending quota increase requests: Look in your Service Quotas console for any pending requests that might be interfering with the process.

6. Contact AWS Support: If none of the above steps resolve the issue, you should contact AWS Support. They can investigate why there's a mismatch between your actual quota and what the SageMaker service is recognizing. They have access to more detailed information about your account and can help resolve such discrepancies.

Remember, even if your quota shows as 30, the error message suggests that the SageMaker service is seeing it as 0. This kind of mismatch typically requires intervention from AWS Support to resolve.
Sources
SageMaker JumpStart question | AWS re:Post
SageMaker ResourceLimitExceeded | AWS re:Post
Troubleshooting - Amazon SageMaker AI