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This likely means that your organization is not in the a supported Federation such as InCommon Federation. You can look up your home organization here to see what its current InCommon status is. It will need to have the 'Federation' tag.
You can learn more about joining the InCommon Federation here.
When your home organization is not available, you can choose to register using a Gmail account or an Internet2 Guest account. See the Registration Guide for more details.
If you organization IS in the InCommon Federation and still not showing up on the list of Identity Providers, it may be set to 'Hide from Discovery'. Please discuss with you Identity Provider operators.
NOTE: If you register a Google or Internet2 Guest account, you will select that respective log in option each time you log in, as opposed to selecting your home institution.
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