Multiple Certificates not working

I am having an issue with using multiple certficiates in the configuration. My Idp sends a response using the first certificate and everything works fine. Sending the same response using the second certificate gets a verifiation error. Both certifcates are valid and have not expired. Both certs are in the referenced folder. See the configuration below:
“PartnerCertificates”:[
{
“Use”:null,
“String”:null,
“FileName”:“certificates\\azure_real1.cer”,
“Password”:null,
“StoreName”:null,
“StoreLocation”:null,
“SerialNumber”:null,
“Thumbprint”:null,
“SubjectName”:null,
“Key”:null
},
{
“Use”:null,
“String”:null,
“FileName”:“certificates\\azure_real2.cer”,
“Password”:null,
“StoreName”:null,
“StoreLocation”:null,
“SerialNumber”:null,
“Thumbprint”:null,
“SubjectName”:null,
“Key”:null
}
]

Not sure what the issue is. Seems like the configuration is setup according to the documentation.
Thanks!

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