Mike:
Sometimes it's not on 'your end' - but the 'other end'. The person receiving your payment may not have a valid e-mail, or there may be some other problem with getting the payment to them.
I had the same problem receiving payments thry PayPal recently. For some reason, the e-mail address that PayPal sent my payment notices to - suddenly wouldn't accept the e-mails. The e-mail program did not notify me of a problem - but as soon as I changed my PayPal account to go to a different e-mail address, everything worked fine.
Go figure ?
Later . . .
Jim
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www.T-waysGraphics.com Always buying Ethyl Globes, Ethyl Single Lenses & Misc Ethyl Items.