Here are some errors that you could encounter when submitting a record for approval or responding to an approval request.
Available in: both Salesforce Classic and Lightning Experience
Available in: Enterprise, Performance, Unlimited, and Developer Editions
This approval request requires the next approver to be determined by the Field Name field. This value is empty.
Salesforce tried to route the approval request based on a hierarchical field, such as Manager. However, the field has no value or specifies an inactive user. This error can occur when a user submits a record for approval or when an approver responds to an approval request.
Required fields are missing: [FieldName].
The approval process includes a field update that fails standard validation rules for the identified field. This error can occur even if the field isn’t visible on your page layout.
Salesforce doesn’t make sure that field updates pass custom validation rules on fields.