You have a valid exemption certificate in CertCapture and Admin Console, but the transaction is calculating tax.
AvaTax and CertCapture
Check to see if this is for an SST State:
A certificate in SST States need to have a Business Type, Tax ID, Tax Number for it to be valid. Once the certificate is updated in CertCapture, re-calculate tax on the transaction in the Admin Console and it should remove the tax.