I would like to add prefilled country code to mobile numbers field in POS for example (Mobile: +61)
I have tried adding (value = "+61") but there was an error: ValueError: Invalid field '' on model 'res.partner'.
t-att-value="prop.mobile || ''" placeholder="" />
i think you are talking about default phone number while creating customer on pos interface.
please note that it is phone field it is not mobile field.
t-att-value="prop.phone || ''" placeholder="" />
if you would like to add mobile field then you have to load mobile field first and add extra input on that xml after phone.
Even if it's prop.phone how would a user add a default value to the field?