Issue in creating or saving the lightning email templates

Hi, When I try to create and save or edit and save an existing lightning email template in sandbox, it's not allowing me to do so, and below errors pop up every time, May I know what's the issue here ?

Error msg :

Template Content :

{{{SBQQ__Quote__c.OwnerFullName}}} has requested your approval for the following quote item with payment terms : {{{SBQQ__Quote__c.SBQQ__PaymentTerms__c}}}.
Quote Amount {{{SBQQ__Quote__c.SBQQ__NetAmount__c}}}
To approve or reject this item click {{{SBQQ__Quote__c.Link}}}