The fiscal sponsor must be a 501(c)(3) organization as recognized by the IRS. The fiscal sponsor cannot be an organization whose tax-exempt status is pending. The sponsored project must be able to qualify for exemption under section 501(c)(3), even if the project has no intention of ever applying for it.
Pressing the Ignore button on the listed invitation on the LinkedIn site is effectively a soft rejection. The message then moves to your Archived folder. You can later choose to open the message again and accept the request.
You don't have to reject any prospective tenants outright or cite reasons for doing so. Be careful if you choose to give reasons for denying tenant applications (we don't recommend doing it at all) - Never quote illegal reasons such as race, color, religion, sex and nationality.