How to allow users to choose multiple options inside of payment field

Is there a way to select multiple services to pay for with the Paypal link? For example, on the link below, if someone wants to select "Provider" and also the "Service Fee". Right now, they can only select one option.

If I understood you correctly you want to allow your users to select more that one option inside of your Paypal field. Currently your Paypal field is set to "Users can choose only one product". You need to change it to "Users can select multiple products". 

After you make this change you users will be able to select multiple options.

Hope this will help. Let us know if you need further assistance.