My goal is to show the not invoiced amount of salesorders grouped by delivery date with a graph.

for this i created a custom field (type float, since we invoice in EUR and CHF and i dont want to mess around with currency problems and for forecasting is this ok) which gets calculated like this:

for record in self:

    record['x_offener_betrag_calc'] = record.amount_total - record.amount_invoiced

the field works properly, i also can aggregate it in lists with sum. but somehow i cant use it in the diagram view. two problems here:

1. i cant select the field in the "values" list and dont find any possibilit to bring it there.

2. if i add filter and adjust the context manually like this:

{'group_by': ['commitment_date:month', 'partner_id'], 'graph_measure': 'x_offener_betrag_calc', 'graph_mode': 'bar', 'graph_groupbys': ['commitment_date:month', 'partner_id'], 'graph_order': None, 'graph_stacked': True}

then i get the following error when applying the filter:

Uncaught Promise > No aggregate function has been provided for the measure 'x_offener_betrag_calc'

has anybody an idea how to make that work?