Inbox Pays, at least for me, doesn’t seem to be worth the time. The cash out threshold is high at $50, and you have to do more than just read emails to get paid. You have to also complete offers. According to PTC Investigation (I site I generally trust for reviews of sites like Inbox Pays), you also have to talk to them on the phone in order to verify your account and get paid.
Fiverr is a popular platform for offering services. You can create your own Gigs to have available for sale. As the name suggests, Gigs are available to purchase starting at $5 though you can offer upsells to increase your earnings. You do need to wait 14 days between completing a Gig to being able to withdraw your earnings by PayPal. There are fees associated with these transactions.