Mystery Shopping Services through the iSS website?
First, they are legitimate, so finding your payment should be possible. Second, the amounts are small, so, no matter what happens, it's not the end of the world (Sometimes folks come to the site with a payment issue and are out hundreds or thousands of dollars.)
They pay through PayPal, using your email address to make sure your funds are directed to the correct PayPal account. Have you looked at your profile information on the iSS site and verified that you have correctly typed in your PayPal email address? (This is a really common blunder.) Also, on what date in March were they paid?
Sometimes a payment can be listed as being made on the iSS site before it actually reaches your account - it could mean that the MSC has processed the payment, but it has not made it through PayPal yet. Once you have done this, contact PayPal and see if they have a record of the payment somewhere. If not, get back to the MSC.
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