contract/agreement_legal/data/ir_sequence.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo noupdate="1">

    <!-- Sequence for agreement -->
    <record id="seq_agreement" model="ir.sequence">
        <field name="name">Agreements</field>
        <field name="code">agreement</field>
        <field name="prefix">AG</field>
        <field name="padding">3</field>
        <field name="company_id" eval="False"/>
    </record>

</odoo>