How can I setup Paypal to accept payments for one-time services as well as a monthly subscription

I have already creatd the paypal payment widget and setup products but I also have a subscription that can be purchased individually and it is mandatory with one of our services. How can this be accomplished. 

It is not possible to get two different kinds of payments in one PayPal payment. I would recommend you to create two new forms which contains only one kind of PayPal payment.

One will contain a PayPal payment for the monthly payment

and the other form will contain for your other products.

Then in your original form you should create two iFrame widgets. In those widgets’ wizards( you can get there clicking the wand image above settings image which are next to the added elements on your form) write the previous two forms individually.

Please do not forget to do this step individually for your previously created forms.

You can change the width and height from setting as it is shown above.

If you want to purchase these two options  you can just skip this step.

To connect them you may consider using “Single-Choice” element in basic section. After you add this element you should use if statements to show them individually.

In addition, please also refer to this guide on How to Create a Basic Multiple Payment form. You can create two PayPal forms (for monthly payment and products) and use the iFrame widget to display those forms in the original form.