Office 365 16.8 Syndication partner scenario. During Office 365 Instance configuration (PCP > Applications > Office 365 v16.8 > Instances > enter instance -Edit) it is not possible to add "Cliend ID", "Secret Key", and "Reseller Tenant Id" because Invitation link field is empty. According to provider's guide for Syndication partner scenario this field should not be mandatory during instance configuration.
This link is configured automatically if parameters "Cliend ID", "Secret Key" and "Reseller Tenant Id" were added during previous update to v16.6. Otherwise, the Invitation link field becomes empty and prevents Instance configuration changes.
Invitation URL is not used in Syndication scenario. Please add any not real link manually, for example, https://not.real.url/