I have a similar problem. But Thumbprint is spelled correctly
vSphere Client version 7.0.3.00700
sdk : vsphere-client-sdk-7.0.3.00000

'

./extension-registration.sh -action registerPlugin --key com.pmc.maxview.maxviewvsphere -url https://vsphere.local/sdk --username administrator@vsphere.local -password 124fgh --version 1.0.0 --vcenterServerThumbprint C8:A0:24:39:B7:10:E1:F9:7B:87:E0:F5:36:AA:C4:48:98:17:EE:82 --pluginUrl https://vsphere.local/catalog/maxView-plugin.zip -serverThumbprint serverThumbprint
'