<group colspan="2" col="2">
<group colspan="4" col="3">
<field name="free_member"/>
- <button name="%(action_membership_invoice_view)d" type="action" string="Join Membership" icon="gtk-apply"/>
+ <button name="%(action_membership_invoice_view)d" type="action" string="Join Membership" attrs="{'readonly':[('free_member','=',True)]}" icon="gtk-apply"/>
<field colspan="4" name="associate_member" attrs="{'invisible':[('membership_state', '!=', 'none')], 'readonly':[('free_member','=',True)]}"/>
<field colspan="4" name="membership_state"/>
</group>