Hi JJLNGRD23,
The SUMIF function is your friend.
Here is one way (the Numbers way IMHO 😎). It uses a single table for the dividend payments, and a single table to sum each month.
In the "Data" table, column A shows dates every two weeks (I assumed that dividends are paid once every two weeks). If that assumption is wrong, it makes no difference to the calculations.
Dates in the "Dividends per Month" table, Column A are formatted as Text. That stops Numbers automatically converting to Date & Time format. Let's keep it simple!

In Column B of both tables, formula in B2: MONTH(A2)
You can hide both Columns B when all is working well.
To sum over each month of a year, the SUMIF function is your friend.
formula in the "Dividends per Month" table, Column C:
SUMIF(Data::B,B2,Data::C)

Hiding the "helper" columns B:

Please reply with questions.
Regards,
Ian.