# Copyright 2017 Eficent Business and IT Consulting Services S.L.
# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).

from odoo import models


class PurchaseOrder(models.Model):
    _name = "purchase.order"
    _inherit = ['purchase.order', 'tier.validation']
    _state_from = ['draft', 'sent']
    _state_to = ['purchase', 'approved']

# Copyright 2017 Eficent Business and IT Consulting Services S.L.
# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).

from odoo import models


class PurchaseOrder(models.Model):
    _name = "purchase.order"
    _inherit = ['purchase.order', 'tier.validation']
    _state_from = ['draft', 'sent', 'to approve']
    _state_to = ['purchase', 'approved']

add the status 'to approve' to the initiating states to trigger the validation.