I have a Power BI model with two tables: one is a "registered user" table and the second is a "user transaction" table. "registered user" table has basic information about a user, e.g. user ID, name, address, phone etc. and the "user transaction" table has rows for each monetary transaction that a user has done, e.g. payment made by users along with the date of the payment. The two tables are joined by the user ID field, which servers as the primary key and has a one-to-many relationship (a user in "registered user" table can have zero or more transactions in the "user transaction" table.)
On a monthly basis, I need to calculate the count of users from the "registered user" table that are non-payers, that is they have no entry in the "user transaction" table. (Or more general would be to define a criteria that they've paid less than some amount.) I am new to power BI and have watched some videos and read some tutorials etc. and am sure that this type of function will require a DAX measure. I'm not sure how to go about it though and can't find a good example that is similar. Any help would be greatly appreciated. Thanks in advance.