If a Bill that was created in Xero gets rejected by an Approver, it goes back to Xero in the "Draft" status. Its Requester needs to amend the Bill in Xero and then resubmit it for approval.
If a Bill that was created in ApprovalMax gets rejected by an Approver, it can be amended, revoked, copied, cancelled, or its approval can be forced.
Administrators can force the approval of rejected Bills:
Requesters can edit Bills and resubmit them for approval: