Count rows from related table (M2M)

Hi,

I have two tables: 'Lead' and "Contact' with relation many to many using keys Lead[ParentContactId] and Contact[ContactId]. I want to create a measure in leads table to count number of matching contact records for each lead based on few criteria:

1. Contact[ContractDate] > Lead[CreatedOn] AND Contact[ContractDate] <= Lead[CreatedOn] + 90
2. if there is no matching contact record or there is no contract for particular contact record (Contact[ContractId] = BLANK()) then show 0

Then I want to split this count equally for each matching lead, so if there are two contact records meeting the criteria for particular lead and two leads with the same 'ParentContactId' then show 1 for each lead.

Each 'Contact' record represents one purchase so that is why contact ids are duplicated. I can group them to get unique records and many to one relation between the tables. I tried it but I have problem with referencing columns that have been grouped as table structured column.

I got to that point and got stuck:

Conversions = 
CALCULATE(
    COUNTROWS(Contact),
    FILTER(
        ALL(Contact),
        COUNTROWS(
            FILTER(
                RELATEDTABLE(Contact),
                Contact[ContractDate] >= Lead[CreatedOn] &&
                Contact[ContractDate] <= Lead[CreatedOn] + 90
            )
        ) > 0
    )
)

I am getting an error: "A single value for column 'CreatedOn' in table 'Lead' cannot be determined. This can happen when a measure formula refers to a column that contains many values without specifying an aggregation such as min, max, count, or sum to get a single result." probably because of many to many relation.

I would be very grateful if someone would like to guide me on how to solve this